W-4 Withholding Calculator
Estimate your federal income tax withholding per paycheck and generate ready-to-use W‑4 entries (Steps 3 and 4). Accurate, mobile‑first, and WCAG-compliant.
W-4 Withholding Calculator
Quickly estimate your federal income tax withholding per paycheck and generate ready-to-use W‑4 entries (Steps 3 and 4). Ideal for employees, HR, and payroll planners who want accurate, transparent figures without guesswork.
Results
Annual wages from this job
$0.00
Estimated AGI (annual)
$0.00
Deduction used (standard or itemized)
$0.00
Taxable income (annual)
$0.00
Federal tax before credits (annual)
$0.00
Child & dependent credits applied (annual)
$0.00
Estimated federal tax (annual, after credits)
$0.00
Estimated federal withholding needed per paycheck (this job)
$0.00
Suggested W‑4 Step 3 (dependents)
$0.00
Suggested W‑4 Step 4(a) (other income)
$0.00
Suggested W‑4 Step 4(b) (deductions exceeding standard)
$0.00
Suggested W‑4 Step 4(c) Extra withholding per paycheck
$0.00
Note: If you provided your current withholding per paycheck, Step 4(c) suggests the incremental amount to reach the target withholding. Otherwise, it displays the full target withholding per paycheck.
Data Source and Methodology
This estimator uses the IRS annualization approach and 2024 tax parameters:
- IRS Publication 15-T (2024) — Federal Income Tax Withholding Methods. Direct PDF
- IRS Publication 505 (2024) — Tax Withholding and Estimated Tax. Reference
- Revenue Procedure 2023-34 — 2024 inflation adjustments (tax brackets). Direct PDF
- Form W‑4 and Instructions (2024). Reference
- IRS Tax Withholding Estimator. Official tool
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Annualize wages and compute AGI:
1) \( W_a = (W_p - P_p)\times n \)
2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \)
3) \( \mathrm{AGI} = W_{\text{total}} + O \)
Deduction used:
4) \( D = \max(\mathrm{SD}_f,\, ID) \)
5) \( TI = \max(0,\, \mathrm{AGI} - D) \)
Progressive tax (piecewise by filing status f):
6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates.
Child & dependent credits with phaseout:
7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \)
8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \)
9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \)
10) \( C = \max(0,\, C_0 - R) \)
11) \( T_{\text{net}} = \max(0,\, T - C) \)
Allocate to this job and convert to per‑paycheck:
12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \)
13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
1) \( W_a = (W_p - P_p)\times n \)
2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \)
3) \( \mathrm{AGI} = W_{\text{total}} + O \)
Deduction used:
4) \( D = \max(\mathrm{SD}_f,\, ID) \)
5) \( TI = \max(0,\, \mathrm{AGI} - D) \)
Progressive tax (piecewise by filing status f):
6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates.
Child & dependent credits with phaseout:
7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \)
8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \)
9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \)
10) \( C = \max(0,\, C_0 - R) \)
11) \( T_{\text{net}} = \max(0,\, T - C) \)
Allocate to this job and convert to per‑paycheck:
12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \)
13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
Glossary of Variables
- Wp: Gross pay per period for this job
- Pp: Pre-tax deductions per period (401k, HSA, etc.)
- n: Pay periods per year (weekly=52, biweekly=26, semimonthly=24, monthly=12, annually=1)
- Wa: Annual wages from this job after pre-tax deductions
- WotherJobs: Annual wages from other job(s) or spouse
- O: Other annual income (interest, dividends, side work)
- SDf: Standard deduction for filing status f
- ID: Itemized deductions total
- TI: Taxable income
- T: Federal tax before credits
- C: Child and dependent credits after phaseout (nonrefundable portion applied)
- Tnet: Net federal tax after credits
- s: Share of total earned income attributable to this job
- Wpp: Estimated withholding needed per paycheck for this job
How It Works: A Step‑by‑Step Example
Scenario: Filing status Single; Biweekly pay (26/yr); Gross per period $3,000; Pre‑tax $200; No other jobs; No other income; Itemized $0; One child under 17; No other dependents.
- Annualize this job: Wa = (3000 − 200) × 26 = $72,800.
- AGI = Wa + WotherJobs + O = 72,800 + 0 + 0 = $72,800.
- Standard deduction (Single, 2024) SD = $14,600. Itemized = $0 → Use $14,600.
- Taxable income TI = 72,800 − 14,600 = $58,200.
- Tax before credits T (2024 Single brackets): 10% of 11,600 = $1,160; 12% of 35,550 (11,600–47,150) = $4,266; 22% of 11,050 (47,150–58,200) = $2,431; Total T ≈ $7,857.
- Credits: C0 = 1 × $2,000 = $2,000. AGI below $200,000 → no phaseout. C = $2,000.
- Tnet = 7,857 − 2,000 = $5,857.
- Share s = Wa / Wa = 1. Per‑paycheck Wpp = 5,857 / 26 ≈ $225.27.
- W‑4 Suggestions: Step 3 = $2,000; Step 4(a) = $0; Step 4(b) = $0 (no excess over standard); If your current withholding is, say, $180, Step 4(c) ≈ 225.27 − 180 = $45.27.
Frequently Asked Questions (FAQ)
Is this calculator compliant with the 2020+ W‑4 design?
Yes. It reflects the current W‑4 structure (Steps 1–5) and provides suggestions for Steps 3 and 4 based on IRS publications.
How accurate is the per‑paycheck estimate?
It uses annualization aligned with IRS guidance and 2024 brackets. Actual payroll systems follow IRS tables, so small differences can occur. Entering other jobs’ wages improves accuracy.
Do you handle the Child Tax Credit phaseout?
Yes. We apply the $50 per $1,000 (or fraction) reduction above $200,000 (Single/HOH) or $400,000 (MFJ), and cap the nonrefundable credit at your tax.
What do I put on Step 4(b)?
Only the amount by which your itemized deductions exceed the standard deduction for your filing status. The calculator shows this value directly.
Where can I verify official figures?
See IRS Publication 15‑T, Publication 505, and the IRS Tax Withholding Estimator linked above. You can also review the W‑4 instructions.
Is this tax advice?
No. This tool is for educational planning. Consult a tax professional for advice about your specific situation.
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[','\]
','
Formula (extracted LaTeX)
\[= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); const money = (n) => new Intl.NumberFormat('en-US', { style:'currency', currency:'USD', maximumFractionDigits:2 }).format(Number.isFinite(n)? n : 0); const clampNonNeg = (v) => isNaN(v)||v<0 ? 0 : v; // Elements const els = { filingStatus:\]
= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); const money = (n) => new Intl.NumberFormat('en-US', { style:'currency', currency:'USD', maximumFractionDigits:2 }).format(Number.isFinite(n)? n : 0); const clampNonNeg = (v) => isNaN(v)||v<0 ? 0 : v; // Elements const els = { filingStatus:
Formula (extracted LaTeX)
\[('.tooltip-btn').forEach(btn => { btn.addEventListener('click', () => { const id = btn.getAttribute('aria-controls'); const panel = document.getElementById(id); const expanded = btn.getAttribute('aria-expanded') === 'true'; btn.setAttribute('aria-expanded', String(!expanded)); panel.setAttribute('aria-hidden', String(expanded)); }); btn.addEventListener('keydown', (e) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); btn.click(); } }); }); // Parameters (2024) const STANDARD_DEDUCTION = { single: 14600, mfj: 29200, hoh: 21900 }; const BRACKETS_2024 = { single: [ [0, 11600, 0.10], [11600, 47150, 0.12], [47150, 100525, 0.22], [100525, 191950, 0.24], [191950, 243725, 0.32], [243725, 609350, 0.35], [609350, Infinity, 0.37] ], mfj: [ [0, 23200, 0.10], [23200, 94300, 0.12], [94300, 201050, 0.22], [201050, 383900, 0.24], [383900, 487450, 0.32], [487450, 731200, 0.35], [731200, Infinity, 0.37] ], hoh: [ [0, 16550, 0.10], [16550, 63100, 0.12], [63100, 100500, 0.22], [100500, 191950, 0.24], [191950, 243700, 0.32], [243700, 609350, 0.35], [609350, Infinity, 0.37] ] }; const CTC_PHASEOUT = { single:200000, hoh:200000, mfj:400000 }; const PERIODS = { weekly: 52, biweekly: 26, semimonthly: 24, monthly: 12, annually: 1 }; function getFilingStatus() { const checked = els.filingStatus.find(r => r.checked); return checked ? checked.value : 'single'; } function getPeriods() { return PERIODS[els.frequency.value] || 26; } // Validation function setError(input, errEl, message) { if (!errEl) return; if (message) { input?.setAttribute('aria-invalid', 'true'); errEl.textContent = message; } else { input?.setAttribute('aria-invalid', 'false'); errEl.textContent = ''; } } function validate() { let ok = true; // frequency if (!PERIODS.hasOwnProperty(els.frequency.value)) { setError(els.frequency, els.freqErr, 'Please choose a valid pay frequency.'); ok = false; } else { setError(els.frequency, els.freqErr, ''); } // gross const gross = parseFloat(els.grossPerPay.value); if (isNaN(gross) || gross <= 0) { setError(els.grossPerPay, els.grossErr, 'Enter a positive gross pay per period (e.g., 3000).'); ok = false; } else { setError(els.grossPerPay, els.grossErr, ''); } // pretax not exceeding gross const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); if (!isNaN(gross) && pretax > gross) { setError(els.pretaxPerPay, els.pretaxErr, 'Pre-tax deductions cannot exceed your gross pay.'); ok = false; } else { setError(els.pretaxPerPay, els.pretaxErr, ''); } // integers for dependents const kids = Number(els.kidsU17.value); const odep = Number(els.otherDeps.value); if (!Number.isInteger(kids) || kids < 0) { setError(els.kidsU17, els.kidsErr, 'Enter a whole number of children under 17 (0 or more).'); ok = false; } else setError(els.kidsU17, els.kidsErr, ''); if (!Number.isInteger(odep) || odep < 0) { setError(els.otherDeps, els.odepsErr, 'Enter a whole number of other dependents (0 or more).'); ok = false; } else setError(els.otherDeps, els.odepsErr, ''); // other numeric fields sanity const fields = [ [els.otherJobsIncome, els.ojErr, 'Enter a non-negative annual amount or leave blank.'], [els.otherIncome, els.oincErr, 'Enter a non-negative annual amount or leave blank.'], [els.itemized, els.itemErr, 'Enter a non-negative annual amount or leave blank.'], [els.currentWithheld, els.cwErr, 'Enter a non-negative amount or leave blank.'] ]; for (const [input, err, msg] of fields) { const val = parseFloat(input.value); if (input.value !== '' && (isNaN(val) || val < 0)) { setError(input, err, msg); ok = false; } else { setError(input, err, ''); } } return ok; } function taxFromBrackets(fstatus, taxable) { const brackets = BRACKETS_2024[fstatus] || BRACKETS_2024.single; let tax = 0; let remaining = taxable; if (remaining <= 0) return 0; for (const [l,u,r] of brackets) { if (remaining <= 0) break; const lower = l; const upper = Math.min(u, taxable); if (upper > lower) { const slice = upper - lower; tax += slice * r; } } return tax; } function compute() { if (!validate()) return; const fstatus = getFilingStatus(); const periods = getPeriods(); const gross = clampNonNeg(parseFloat(els.grossPerPay.value)); const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); const otherJobs = clampNonNeg(parseFloat(els.otherJobsIncome.value)); const otherInc = clampNonNeg(parseFloat(els.otherIncome.value)); const itemized = clampNonNeg(parseFloat(els.itemized.value)); const kids = clampNonNeg(parseFloat(els.kidsU17.value)); const odep = clampNonNeg(parseFloat(els.otherDeps.value)); const currentWithheld = clampNonNeg(parseFloat(els.currentWithheld.value)); const taxablePerPay = Math.max(0, gross - pretax); const annualThisJob = taxablePerPay * periods; const totalEarned = annualThisJob + otherJobs; const AGI = totalEarned + otherInc; const stdDed = STANDARD_DEDUCTION[fstatus] || STANDARD_DEDUCTION.single; const deductionUsed = Math.max(stdDed, itemized); const taxableIncome = Math.max(0, AGI - deductionUsed); const taxBefore = taxFromBrackets(fstatus, taxableIncome); // Credits const baseCredit = 2000 * Math.round(kids) + 500 * Math.round(odep); const phaseThr = CTC_PHASEOUT[fstatus] || 200000; const excess = Math.max(0, AGI - phaseThr); const reduction = excess > 0 ? 50 * Math.ceil(excess / 1000) : 0; const creditAfterPhase = Math.max(0, baseCredit - reduction); const creditApplied = Math.min(creditAfterPhase, taxBefore); const taxAfter = Math.max(0, taxBefore - creditApplied); // Allocation to this job const share = totalEarned > 0 ? (annualThisJob / totalEarned) : 1; const perPayNeeded = (taxAfter * share) / Math.max(1, periods); // W-4 suggestions const step3 = baseCredit; // Amount entered on Step 3 equals estimated nonrefundable credits total const step4a = otherInc; // as entered const step4b = Math.max(0, itemized - stdDed); // excess over standard let step4c; // per paycheck extra withholding if (currentWithheld > 0) { step4c = Math.max(0, perPayNeeded - currentWithheld); } else { // If user doesn't know current withholding, show full target per-pay withholding as a conservative guide step4c = perPayNeeded; } // Update UI els.resAnnualThis.textContent = money(annualThisJob); els.resAGI.textContent = money(AGI); els.resDeductionUsed.textContent = money(deductionUsed); els.resTaxable.textContent = money(taxableIncome); els.resTaxBefore.textContent = money(taxBefore); els.resCredits.textContent = money(creditApplied); els.resTaxAfter.textContent = money(taxAfter); els.resPerPay.textContent = money(perPayNeeded); els.resStep3.textContent = money(step3); els.resStep4a.textContent = money(step4a); els.resStep4b.textContent = money(step4b); els.resStep4c.textContent = money(step4c); } // Events ['blur','change','input'].forEach(ev => { els.grossPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.pretaxPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherJobsIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.itemized.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.kidsU17.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherDeps.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.currentWithheld.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); }); els.frequency.addEventListener('change', () => { validate(); compute(); }); els.filingStatus.forEach(r => r.addEventListener('change', () => { validate(); compute(); })); els.calcBtn.addEventListener('click', compute); els.resetBtn.addEventListener('click', () => { $('#fsSingle').checked = true; els.frequency.value = 'biweekly'; els.grossPerPay.value = ''; els.pretaxPerPay.value = ''; els.otherJobsIncome.value = ''; els.otherIncome.value = ''; els.itemized.value = ''; els.kidsU17.value = '0'; els.otherDeps.value = '0'; els.currentWithheld.value = ''; // clear errors [els.freqErr, els.grossErr, els.pretaxErr, els.ojErr, els.oincErr, els.itemErr, els.kidsErr, els.odepsErr, els.cwErr].forEach(e => e.textContent = '');\]
('.tooltip-btn').forEach(btn => { btn.addEventListener('click', () => { const id = btn.getAttribute('aria-controls'); const panel = document.getElementById(id); const expanded = btn.getAttribute('aria-expanded') === 'true'; btn.setAttribute('aria-expanded', String(!expanded)); panel.setAttribute('aria-hidden', String(expanded)); }); btn.addEventListener('keydown', (e) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); btn.click(); } }); }); // Parameters (2024) const STANDARD_DEDUCTION = { single: 14600, mfj: 29200, hoh: 21900 }; const BRACKETS_2024 = { single: [ [0, 11600, 0.10], [11600, 47150, 0.12], [47150, 100525, 0.22], [100525, 191950, 0.24], [191950, 243725, 0.32], [243725, 609350, 0.35], [609350, Infinity, 0.37] ], mfj: [ [0, 23200, 0.10], [23200, 94300, 0.12], [94300, 201050, 0.22], [201050, 383900, 0.24], [383900, 487450, 0.32], [487450, 731200, 0.35], [731200, Infinity, 0.37] ], hoh: [ [0, 16550, 0.10], [16550, 63100, 0.12], [63100, 100500, 0.22], [100500, 191950, 0.24], [191950, 243700, 0.32], [243700, 609350, 0.35], [609350, Infinity, 0.37] ] }; const CTC_PHASEOUT = { single:200000, hoh:200000, mfj:400000 }; const PERIODS = { weekly: 52, biweekly: 26, semimonthly: 24, monthly: 12, annually: 1 }; function getFilingStatus() { const checked = els.filingStatus.find(r => r.checked); return checked ? checked.value : 'single'; } function getPeriods() { return PERIODS[els.frequency.value] || 26; } // Validation function setError(input, errEl, message) { if (!errEl) return; if (message) { input?.setAttribute('aria-invalid', 'true'); errEl.textContent = message; } else { input?.setAttribute('aria-invalid', 'false'); errEl.textContent = ''; } } function validate() { let ok = true; // frequency if (!PERIODS.hasOwnProperty(els.frequency.value)) { setError(els.frequency, els.freqErr, 'Please choose a valid pay frequency.'); ok = false; } else { setError(els.frequency, els.freqErr, ''); } // gross const gross = parseFloat(els.grossPerPay.value); if (isNaN(gross) || gross <= 0) { setError(els.grossPerPay, els.grossErr, 'Enter a positive gross pay per period (e.g., 3000).'); ok = false; } else { setError(els.grossPerPay, els.grossErr, ''); } // pretax not exceeding gross const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); if (!isNaN(gross) && pretax > gross) { setError(els.pretaxPerPay, els.pretaxErr, 'Pre-tax deductions cannot exceed your gross pay.'); ok = false; } else { setError(els.pretaxPerPay, els.pretaxErr, ''); } // integers for dependents const kids = Number(els.kidsU17.value); const odep = Number(els.otherDeps.value); if (!Number.isInteger(kids) || kids < 0) { setError(els.kidsU17, els.kidsErr, 'Enter a whole number of children under 17 (0 or more).'); ok = false; } else setError(els.kidsU17, els.kidsErr, ''); if (!Number.isInteger(odep) || odep < 0) { setError(els.otherDeps, els.odepsErr, 'Enter a whole number of other dependents (0 or more).'); ok = false; } else setError(els.otherDeps, els.odepsErr, ''); // other numeric fields sanity const fields = [ [els.otherJobsIncome, els.ojErr, 'Enter a non-negative annual amount or leave blank.'], [els.otherIncome, els.oincErr, 'Enter a non-negative annual amount or leave blank.'], [els.itemized, els.itemErr, 'Enter a non-negative annual amount or leave blank.'], [els.currentWithheld, els.cwErr, 'Enter a non-negative amount or leave blank.'] ]; for (const [input, err, msg] of fields) { const val = parseFloat(input.value); if (input.value !== '' && (isNaN(val) || val < 0)) { setError(input, err, msg); ok = false; } else { setError(input, err, ''); } } return ok; } function taxFromBrackets(fstatus, taxable) { const brackets = BRACKETS_2024[fstatus] || BRACKETS_2024.single; let tax = 0; let remaining = taxable; if (remaining <= 0) return 0; for (const [l,u,r] of brackets) { if (remaining <= 0) break; const lower = l; const upper = Math.min(u, taxable); if (upper > lower) { const slice = upper - lower; tax += slice * r; } } return tax; } function compute() { if (!validate()) return; const fstatus = getFilingStatus(); const periods = getPeriods(); const gross = clampNonNeg(parseFloat(els.grossPerPay.value)); const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); const otherJobs = clampNonNeg(parseFloat(els.otherJobsIncome.value)); const otherInc = clampNonNeg(parseFloat(els.otherIncome.value)); const itemized = clampNonNeg(parseFloat(els.itemized.value)); const kids = clampNonNeg(parseFloat(els.kidsU17.value)); const odep = clampNonNeg(parseFloat(els.otherDeps.value)); const currentWithheld = clampNonNeg(parseFloat(els.currentWithheld.value)); const taxablePerPay = Math.max(0, gross - pretax); const annualThisJob = taxablePerPay * periods; const totalEarned = annualThisJob + otherJobs; const AGI = totalEarned + otherInc; const stdDed = STANDARD_DEDUCTION[fstatus] || STANDARD_DEDUCTION.single; const deductionUsed = Math.max(stdDed, itemized); const taxableIncome = Math.max(0, AGI - deductionUsed); const taxBefore = taxFromBrackets(fstatus, taxableIncome); // Credits const baseCredit = 2000 * Math.round(kids) + 500 * Math.round(odep); const phaseThr = CTC_PHASEOUT[fstatus] || 200000; const excess = Math.max(0, AGI - phaseThr); const reduction = excess > 0 ? 50 * Math.ceil(excess / 1000) : 0; const creditAfterPhase = Math.max(0, baseCredit - reduction); const creditApplied = Math.min(creditAfterPhase, taxBefore); const taxAfter = Math.max(0, taxBefore - creditApplied); // Allocation to this job const share = totalEarned > 0 ? (annualThisJob / totalEarned) : 1; const perPayNeeded = (taxAfter * share) / Math.max(1, periods); // W-4 suggestions const step3 = baseCredit; // Amount entered on Step 3 equals estimated nonrefundable credits total const step4a = otherInc; // as entered const step4b = Math.max(0, itemized - stdDed); // excess over standard let step4c; // per paycheck extra withholding if (currentWithheld > 0) { step4c = Math.max(0, perPayNeeded - currentWithheld); } else { // If user doesn't know current withholding, show full target per-pay withholding as a conservative guide step4c = perPayNeeded; } // Update UI els.resAnnualThis.textContent = money(annualThisJob); els.resAGI.textContent = money(AGI); els.resDeductionUsed.textContent = money(deductionUsed); els.resTaxable.textContent = money(taxableIncome); els.resTaxBefore.textContent = money(taxBefore); els.resCredits.textContent = money(creditApplied); els.resTaxAfter.textContent = money(taxAfter); els.resPerPay.textContent = money(perPayNeeded); els.resStep3.textContent = money(step3); els.resStep4a.textContent = money(step4a); els.resStep4b.textContent = money(step4b); els.resStep4c.textContent = money(step4c); } // Events ['blur','change','input'].forEach(ev => { els.grossPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.pretaxPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherJobsIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.itemized.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.kidsU17.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherDeps.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.currentWithheld.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); }); els.frequency.addEventListener('change', () => { validate(); compute(); }); els.filingStatus.forEach(r => r.addEventListener('change', () => { validate(); compute(); })); els.calcBtn.addEventListener('click', compute); els.resetBtn.addEventListener('click', () => { $('#fsSingle').checked = true; els.frequency.value = 'biweekly'; els.grossPerPay.value = ''; els.pretaxPerPay.value = ''; els.otherJobsIncome.value = ''; els.otherIncome.value = ''; els.itemized.value = ''; els.kidsU17.value = '0'; els.otherDeps.value = '0'; els.currentWithheld.value = ''; // clear errors [els.freqErr, els.grossErr, els.pretaxErr, els.ojErr, els.oincErr, els.itemErr, els.kidsErr, els.odepsErr, els.cwErr].forEach(e => e.textContent = '');
Formula (extracted text)
Annualize wages and compute AGI: 1) \( W_a = (W_p - P_p)\times n \) 2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \) 3) \( \mathrm{AGI} = W_{\text{total}} + O \) Deduction used: 4) \( D = \max(\mathrm{SD}_f,\, ID) \) 5) \( TI = \max(0,\, \mathrm{AGI} - D) \) Progressive tax (piecewise by filing status f): 6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates. Child & dependent credits with phaseout: 7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \) 8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \) 9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \) 10) \( C = \max(0,\, C_0 - R) \) 11) \( T_{\text{net}} = \max(0,\, T - C) \) Allocate to this job and convert to per‑paycheck: 12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \) 13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
Variables and units
- T = property tax (annual or monthly depending on input) (currency)
- I = homeowners insurance (annual or monthly depending on input) (currency)
Sources (authoritative):
- Direct PDF — irs.gov · Accessed 2026-01-19
https://www.irs.gov/pub/irs-pdf/p15t.pdf - Reference — irs.gov · Accessed 2026-01-19
https://www.irs.gov/forms-pubs/about-publication-505 - Direct PDF — irs.gov · Accessed 2026-01-19
https://www.irs.gov/pub/irs-drop/rp-23-34.pdf - Reference — irs.gov · Accessed 2026-01-19
https://www.irs.gov/forms-pubs/about-form-w-4 - Official tool — irs.gov · Accessed 2026-01-19
https://www.irs.gov/individuals/tax-withholding-estimator
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.
Full original guide (expanded)
Skip to main contentSkip to main contentW-4 Withholding Calculator
Quickly estimate your federal income tax withholding per paycheck and generate ready-to-use W‑4 entries (Steps 3 and 4). Ideal for employees, HR, and payroll planners who want accurate, transparent figures without guesswork.
Results
Annual wages from this job
$0.00
Estimated AGI (annual)
$0.00
Deduction used (standard or itemized)
$0.00
Taxable income (annual)
$0.00
Federal tax before credits (annual)
$0.00
Child & dependent credits applied (annual)
$0.00
Estimated federal tax (annual, after credits)
$0.00
Estimated federal withholding needed per paycheck (this job)
$0.00
Suggested W‑4 Step 3 (dependents)
$0.00
Suggested W‑4 Step 4(a) (other income)
$0.00
Suggested W‑4 Step 4(b) (deductions exceeding standard)
$0.00
Suggested W‑4 Step 4(c) Extra withholding per paycheck
$0.00
Note: If you provided your current withholding per paycheck, Step 4(c) suggests the incremental amount to reach the target withholding. Otherwise, it displays the full target withholding per paycheck.
Data Source and Methodology
This estimator uses the IRS annualization approach and 2024 tax parameters:
- IRS Publication 15-T (2024) — Federal Income Tax Withholding Methods. Direct PDF
- IRS Publication 505 (2024) — Tax Withholding and Estimated Tax. Reference
- Revenue Procedure 2023-34 — 2024 inflation adjustments (tax brackets). Direct PDF
- Form W‑4 and Instructions (2024). Reference
- IRS Tax Withholding Estimator. Official tool
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Annualize wages and compute AGI:
1) \( W_a = (W_p - P_p)\times n \)
2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \)
3) \( \mathrm{AGI} = W_{\text{total}} + O \)
Deduction used:
4) \( D = \max(\mathrm{SD}_f,\, ID) \)
5) \( TI = \max(0,\, \mathrm{AGI} - D) \)
Progressive tax (piecewise by filing status f):
6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates.
Child & dependent credits with phaseout:
7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \)
8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \)
9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \)
10) \( C = \max(0,\, C_0 - R) \)
11) \( T_{\text{net}} = \max(0,\, T - C) \)
Allocate to this job and convert to per‑paycheck:
12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \)
13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
1) \( W_a = (W_p - P_p)\times n \)
2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \)
3) \( \mathrm{AGI} = W_{\text{total}} + O \)
Deduction used:
4) \( D = \max(\mathrm{SD}_f,\, ID) \)
5) \( TI = \max(0,\, \mathrm{AGI} - D) \)
Progressive tax (piecewise by filing status f):
6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates.
Child & dependent credits with phaseout:
7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \)
8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \)
9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \)
10) \( C = \max(0,\, C_0 - R) \)
11) \( T_{\text{net}} = \max(0,\, T - C) \)
Allocate to this job and convert to per‑paycheck:
12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \)
13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
Glossary of Variables
- Wp: Gross pay per period for this job
- Pp: Pre-tax deductions per period (401k, HSA, etc.)
- n: Pay periods per year (weekly=52, biweekly=26, semimonthly=24, monthly=12, annually=1)
- Wa: Annual wages from this job after pre-tax deductions
- WotherJobs: Annual wages from other job(s) or spouse
- O: Other annual income (interest, dividends, side work)
- SDf: Standard deduction for filing status f
- ID: Itemized deductions total
- TI: Taxable income
- T: Federal tax before credits
- C: Child and dependent credits after phaseout (nonrefundable portion applied)
- Tnet: Net federal tax after credits
- s: Share of total earned income attributable to this job
- Wpp: Estimated withholding needed per paycheck for this job
How It Works: A Step‑by‑Step Example
Scenario: Filing status Single; Biweekly pay (26/yr); Gross per period $3,000; Pre‑tax $200; No other jobs; No other income; Itemized $0; One child under 17; No other dependents.
- Annualize this job: Wa = (3000 − 200) × 26 = $72,800.
- AGI = Wa + WotherJobs + O = 72,800 + 0 + 0 = $72,800.
- Standard deduction (Single, 2024) SD = $14,600. Itemized = $0 → Use $14,600.
- Taxable income TI = 72,800 − 14,600 = $58,200.
- Tax before credits T (2024 Single brackets): 10% of 11,600 = $1,160; 12% of 35,550 (11,600–47,150) = $4,266; 22% of 11,050 (47,150–58,200) = $2,431; Total T ≈ $7,857.
- Credits: C0 = 1 × $2,000 = $2,000. AGI below $200,000 → no phaseout. C = $2,000.
- Tnet = 7,857 − 2,000 = $5,857.
- Share s = Wa / Wa = 1. Per‑paycheck Wpp = 5,857 / 26 ≈ $225.27.
- W‑4 Suggestions: Step 3 = $2,000; Step 4(a) = $0; Step 4(b) = $0 (no excess over standard); If your current withholding is, say, $180, Step 4(c) ≈ 225.27 − 180 = $45.27.
Frequently Asked Questions (FAQ)
Is this calculator compliant with the 2020+ W‑4 design?
Yes. It reflects the current W‑4 structure (Steps 1–5) and provides suggestions for Steps 3 and 4 based on IRS publications.
How accurate is the per‑paycheck estimate?
It uses annualization aligned with IRS guidance and 2024 brackets. Actual payroll systems follow IRS tables, so small differences can occur. Entering other jobs’ wages improves accuracy.
Do you handle the Child Tax Credit phaseout?
Yes. We apply the $50 per $1,000 (or fraction) reduction above $200,000 (Single/HOH) or $400,000 (MFJ), and cap the nonrefundable credit at your tax.
What do I put on Step 4(b)?
Only the amount by which your itemized deductions exceed the standard deduction for your filing status. The calculator shows this value directly.
Where can I verify official figures?
See IRS Publication 15‑T, Publication 505, and the IRS Tax Withholding Estimator linked above. You can also review the W‑4 instructions.
Is this tax advice?
No. This tool is for educational planning. Consult a tax professional for advice about your specific situation.
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[','\]
','
Formula (extracted LaTeX)
\[= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); const money = (n) => new Intl.NumberFormat('en-US', { style:'currency', currency:'USD', maximumFractionDigits:2 }).format(Number.isFinite(n)? n : 0); const clampNonNeg = (v) => isNaN(v)||v<0 ? 0 : v; // Elements const els = { filingStatus:\]
= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); const money = (n) => new Intl.NumberFormat('en-US', { style:'currency', currency:'USD', maximumFractionDigits:2 }).format(Number.isFinite(n)? n : 0); const clampNonNeg = (v) => isNaN(v)||v<0 ? 0 : v; // Elements const els = { filingStatus:
Formula (extracted LaTeX)
\[('.tooltip-btn').forEach(btn => { btn.addEventListener('click', () => { const id = btn.getAttribute('aria-controls'); const panel = document.getElementById(id); const expanded = btn.getAttribute('aria-expanded') === 'true'; btn.setAttribute('aria-expanded', String(!expanded)); panel.setAttribute('aria-hidden', String(expanded)); }); btn.addEventListener('keydown', (e) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); btn.click(); } }); }); // Parameters (2024) const STANDARD_DEDUCTION = { single: 14600, mfj: 29200, hoh: 21900 }; const BRACKETS_2024 = { single: [ [0, 11600, 0.10], [11600, 47150, 0.12], [47150, 100525, 0.22], [100525, 191950, 0.24], [191950, 243725, 0.32], [243725, 609350, 0.35], [609350, Infinity, 0.37] ], mfj: [ [0, 23200, 0.10], [23200, 94300, 0.12], [94300, 201050, 0.22], [201050, 383900, 0.24], [383900, 487450, 0.32], [487450, 731200, 0.35], [731200, Infinity, 0.37] ], hoh: [ [0, 16550, 0.10], [16550, 63100, 0.12], [63100, 100500, 0.22], [100500, 191950, 0.24], [191950, 243700, 0.32], [243700, 609350, 0.35], [609350, Infinity, 0.37] ] }; const CTC_PHASEOUT = { single:200000, hoh:200000, mfj:400000 }; const PERIODS = { weekly: 52, biweekly: 26, semimonthly: 24, monthly: 12, annually: 1 }; function getFilingStatus() { const checked = els.filingStatus.find(r => r.checked); return checked ? checked.value : 'single'; } function getPeriods() { return PERIODS[els.frequency.value] || 26; } // Validation function setError(input, errEl, message) { if (!errEl) return; if (message) { input?.setAttribute('aria-invalid', 'true'); errEl.textContent = message; } else { input?.setAttribute('aria-invalid', 'false'); errEl.textContent = ''; } } function validate() { let ok = true; // frequency if (!PERIODS.hasOwnProperty(els.frequency.value)) { setError(els.frequency, els.freqErr, 'Please choose a valid pay frequency.'); ok = false; } else { setError(els.frequency, els.freqErr, ''); } // gross const gross = parseFloat(els.grossPerPay.value); if (isNaN(gross) || gross <= 0) { setError(els.grossPerPay, els.grossErr, 'Enter a positive gross pay per period (e.g., 3000).'); ok = false; } else { setError(els.grossPerPay, els.grossErr, ''); } // pretax not exceeding gross const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); if (!isNaN(gross) && pretax > gross) { setError(els.pretaxPerPay, els.pretaxErr, 'Pre-tax deductions cannot exceed your gross pay.'); ok = false; } else { setError(els.pretaxPerPay, els.pretaxErr, ''); } // integers for dependents const kids = Number(els.kidsU17.value); const odep = Number(els.otherDeps.value); if (!Number.isInteger(kids) || kids < 0) { setError(els.kidsU17, els.kidsErr, 'Enter a whole number of children under 17 (0 or more).'); ok = false; } else setError(els.kidsU17, els.kidsErr, ''); if (!Number.isInteger(odep) || odep < 0) { setError(els.otherDeps, els.odepsErr, 'Enter a whole number of other dependents (0 or more).'); ok = false; } else setError(els.otherDeps, els.odepsErr, ''); // other numeric fields sanity const fields = [ [els.otherJobsIncome, els.ojErr, 'Enter a non-negative annual amount or leave blank.'], [els.otherIncome, els.oincErr, 'Enter a non-negative annual amount or leave blank.'], [els.itemized, els.itemErr, 'Enter a non-negative annual amount or leave blank.'], [els.currentWithheld, els.cwErr, 'Enter a non-negative amount or leave blank.'] ]; for (const [input, err, msg] of fields) { const val = parseFloat(input.value); if (input.value !== '' && (isNaN(val) || val < 0)) { setError(input, err, msg); ok = false; } else { setError(input, err, ''); } } return ok; } function taxFromBrackets(fstatus, taxable) { const brackets = BRACKETS_2024[fstatus] || BRACKETS_2024.single; let tax = 0; let remaining = taxable; if (remaining <= 0) return 0; for (const [l,u,r] of brackets) { if (remaining <= 0) break; const lower = l; const upper = Math.min(u, taxable); if (upper > lower) { const slice = upper - lower; tax += slice * r; } } return tax; } function compute() { if (!validate()) return; const fstatus = getFilingStatus(); const periods = getPeriods(); const gross = clampNonNeg(parseFloat(els.grossPerPay.value)); const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); const otherJobs = clampNonNeg(parseFloat(els.otherJobsIncome.value)); const otherInc = clampNonNeg(parseFloat(els.otherIncome.value)); const itemized = clampNonNeg(parseFloat(els.itemized.value)); const kids = clampNonNeg(parseFloat(els.kidsU17.value)); const odep = clampNonNeg(parseFloat(els.otherDeps.value)); const currentWithheld = clampNonNeg(parseFloat(els.currentWithheld.value)); const taxablePerPay = Math.max(0, gross - pretax); const annualThisJob = taxablePerPay * periods; const totalEarned = annualThisJob + otherJobs; const AGI = totalEarned + otherInc; const stdDed = STANDARD_DEDUCTION[fstatus] || STANDARD_DEDUCTION.single; const deductionUsed = Math.max(stdDed, itemized); const taxableIncome = Math.max(0, AGI - deductionUsed); const taxBefore = taxFromBrackets(fstatus, taxableIncome); // Credits const baseCredit = 2000 * Math.round(kids) + 500 * Math.round(odep); const phaseThr = CTC_PHASEOUT[fstatus] || 200000; const excess = Math.max(0, AGI - phaseThr); const reduction = excess > 0 ? 50 * Math.ceil(excess / 1000) : 0; const creditAfterPhase = Math.max(0, baseCredit - reduction); const creditApplied = Math.min(creditAfterPhase, taxBefore); const taxAfter = Math.max(0, taxBefore - creditApplied); // Allocation to this job const share = totalEarned > 0 ? (annualThisJob / totalEarned) : 1; const perPayNeeded = (taxAfter * share) / Math.max(1, periods); // W-4 suggestions const step3 = baseCredit; // Amount entered on Step 3 equals estimated nonrefundable credits total const step4a = otherInc; // as entered const step4b = Math.max(0, itemized - stdDed); // excess over standard let step4c; // per paycheck extra withholding if (currentWithheld > 0) { step4c = Math.max(0, perPayNeeded - currentWithheld); } else { // If user doesn't know current withholding, show full target per-pay withholding as a conservative guide step4c = perPayNeeded; } // Update UI els.resAnnualThis.textContent = money(annualThisJob); els.resAGI.textContent = money(AGI); els.resDeductionUsed.textContent = money(deductionUsed); els.resTaxable.textContent = money(taxableIncome); els.resTaxBefore.textContent = money(taxBefore); els.resCredits.textContent = money(creditApplied); els.resTaxAfter.textContent = money(taxAfter); els.resPerPay.textContent = money(perPayNeeded); els.resStep3.textContent = money(step3); els.resStep4a.textContent = money(step4a); els.resStep4b.textContent = money(step4b); els.resStep4c.textContent = money(step4c); } // Events ['blur','change','input'].forEach(ev => { els.grossPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.pretaxPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherJobsIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.itemized.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.kidsU17.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherDeps.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.currentWithheld.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); }); els.frequency.addEventListener('change', () => { validate(); compute(); }); els.filingStatus.forEach(r => r.addEventListener('change', () => { validate(); compute(); })); els.calcBtn.addEventListener('click', compute); els.resetBtn.addEventListener('click', () => { $('#fsSingle').checked = true; els.frequency.value = 'biweekly'; els.grossPerPay.value = ''; els.pretaxPerPay.value = ''; els.otherJobsIncome.value = ''; els.otherIncome.value = ''; els.itemized.value = ''; els.kidsU17.value = '0'; els.otherDeps.value = '0'; els.currentWithheld.value = ''; // clear errors [els.freqErr, els.grossErr, els.pretaxErr, els.ojErr, els.oincErr, els.itemErr, els.kidsErr, els.odepsErr, els.cwErr].forEach(e => e.textContent = '');\]
('.tooltip-btn').forEach(btn => { btn.addEventListener('click', () => { const id = btn.getAttribute('aria-controls'); const panel = document.getElementById(id); const expanded = btn.getAttribute('aria-expanded') === 'true'; btn.setAttribute('aria-expanded', String(!expanded)); panel.setAttribute('aria-hidden', String(expanded)); }); btn.addEventListener('keydown', (e) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); btn.click(); } }); }); // Parameters (2024) const STANDARD_DEDUCTION = { single: 14600, mfj: 29200, hoh: 21900 }; const BRACKETS_2024 = { single: [ [0, 11600, 0.10], [11600, 47150, 0.12], [47150, 100525, 0.22], [100525, 191950, 0.24], [191950, 243725, 0.32], [243725, 609350, 0.35], [609350, Infinity, 0.37] ], mfj: [ [0, 23200, 0.10], [23200, 94300, 0.12], [94300, 201050, 0.22], [201050, 383900, 0.24], [383900, 487450, 0.32], [487450, 731200, 0.35], [731200, Infinity, 0.37] ], hoh: [ [0, 16550, 0.10], [16550, 63100, 0.12], [63100, 100500, 0.22], [100500, 191950, 0.24], [191950, 243700, 0.32], [243700, 609350, 0.35], [609350, Infinity, 0.37] ] }; const CTC_PHASEOUT = { single:200000, hoh:200000, mfj:400000 }; const PERIODS = { weekly: 52, biweekly: 26, semimonthly: 24, monthly: 12, annually: 1 }; function getFilingStatus() { const checked = els.filingStatus.find(r => r.checked); return checked ? checked.value : 'single'; } function getPeriods() { return PERIODS[els.frequency.value] || 26; } // Validation function setError(input, errEl, message) { if (!errEl) return; if (message) { input?.setAttribute('aria-invalid', 'true'); errEl.textContent = message; } else { input?.setAttribute('aria-invalid', 'false'); errEl.textContent = ''; } } function validate() { let ok = true; // frequency if (!PERIODS.hasOwnProperty(els.frequency.value)) { setError(els.frequency, els.freqErr, 'Please choose a valid pay frequency.'); ok = false; } else { setError(els.frequency, els.freqErr, ''); } // gross const gross = parseFloat(els.grossPerPay.value); if (isNaN(gross) || gross <= 0) { setError(els.grossPerPay, els.grossErr, 'Enter a positive gross pay per period (e.g., 3000).'); ok = false; } else { setError(els.grossPerPay, els.grossErr, ''); } // pretax not exceeding gross const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); if (!isNaN(gross) && pretax > gross) { setError(els.pretaxPerPay, els.pretaxErr, 'Pre-tax deductions cannot exceed your gross pay.'); ok = false; } else { setError(els.pretaxPerPay, els.pretaxErr, ''); } // integers for dependents const kids = Number(els.kidsU17.value); const odep = Number(els.otherDeps.value); if (!Number.isInteger(kids) || kids < 0) { setError(els.kidsU17, els.kidsErr, 'Enter a whole number of children under 17 (0 or more).'); ok = false; } else setError(els.kidsU17, els.kidsErr, ''); if (!Number.isInteger(odep) || odep < 0) { setError(els.otherDeps, els.odepsErr, 'Enter a whole number of other dependents (0 or more).'); ok = false; } else setError(els.otherDeps, els.odepsErr, ''); // other numeric fields sanity const fields = [ [els.otherJobsIncome, els.ojErr, 'Enter a non-negative annual amount or leave blank.'], [els.otherIncome, els.oincErr, 'Enter a non-negative annual amount or leave blank.'], [els.itemized, els.itemErr, 'Enter a non-negative annual amount or leave blank.'], [els.currentWithheld, els.cwErr, 'Enter a non-negative amount or leave blank.'] ]; for (const [input, err, msg] of fields) { const val = parseFloat(input.value); if (input.value !== '' && (isNaN(val) || val < 0)) { setError(input, err, msg); ok = false; } else { setError(input, err, ''); } } return ok; } function taxFromBrackets(fstatus, taxable) { const brackets = BRACKETS_2024[fstatus] || BRACKETS_2024.single; let tax = 0; let remaining = taxable; if (remaining <= 0) return 0; for (const [l,u,r] of brackets) { if (remaining <= 0) break; const lower = l; const upper = Math.min(u, taxable); if (upper > lower) { const slice = upper - lower; tax += slice * r; } } return tax; } function compute() { if (!validate()) return; const fstatus = getFilingStatus(); const periods = getPeriods(); const gross = clampNonNeg(parseFloat(els.grossPerPay.value)); const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); const otherJobs = clampNonNeg(parseFloat(els.otherJobsIncome.value)); const otherInc = clampNonNeg(parseFloat(els.otherIncome.value)); const itemized = clampNonNeg(parseFloat(els.itemized.value)); const kids = clampNonNeg(parseFloat(els.kidsU17.value)); const odep = clampNonNeg(parseFloat(els.otherDeps.value)); const currentWithheld = clampNonNeg(parseFloat(els.currentWithheld.value)); const taxablePerPay = Math.max(0, gross - pretax); const annualThisJob = taxablePerPay * periods; const totalEarned = annualThisJob + otherJobs; const AGI = totalEarned + otherInc; const stdDed = STANDARD_DEDUCTION[fstatus] || STANDARD_DEDUCTION.single; const deductionUsed = Math.max(stdDed, itemized); const taxableIncome = Math.max(0, AGI - deductionUsed); const taxBefore = taxFromBrackets(fstatus, taxableIncome); // Credits const baseCredit = 2000 * Math.round(kids) + 500 * Math.round(odep); const phaseThr = CTC_PHASEOUT[fstatus] || 200000; const excess = Math.max(0, AGI - phaseThr); const reduction = excess > 0 ? 50 * Math.ceil(excess / 1000) : 0; const creditAfterPhase = Math.max(0, baseCredit - reduction); const creditApplied = Math.min(creditAfterPhase, taxBefore); const taxAfter = Math.max(0, taxBefore - creditApplied); // Allocation to this job const share = totalEarned > 0 ? (annualThisJob / totalEarned) : 1; const perPayNeeded = (taxAfter * share) / Math.max(1, periods); // W-4 suggestions const step3 = baseCredit; // Amount entered on Step 3 equals estimated nonrefundable credits total const step4a = otherInc; // as entered const step4b = Math.max(0, itemized - stdDed); // excess over standard let step4c; // per paycheck extra withholding if (currentWithheld > 0) { step4c = Math.max(0, perPayNeeded - currentWithheld); } else { // If user doesn't know current withholding, show full target per-pay withholding as a conservative guide step4c = perPayNeeded; } // Update UI els.resAnnualThis.textContent = money(annualThisJob); els.resAGI.textContent = money(AGI); els.resDeductionUsed.textContent = money(deductionUsed); els.resTaxable.textContent = money(taxableIncome); els.resTaxBefore.textContent = money(taxBefore); els.resCredits.textContent = money(creditApplied); els.resTaxAfter.textContent = money(taxAfter); els.resPerPay.textContent = money(perPayNeeded); els.resStep3.textContent = money(step3); els.resStep4a.textContent = money(step4a); els.resStep4b.textContent = money(step4b); els.resStep4c.textContent = money(step4c); } // Events ['blur','change','input'].forEach(ev => { els.grossPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.pretaxPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherJobsIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.itemized.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.kidsU17.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherDeps.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.currentWithheld.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); }); els.frequency.addEventListener('change', () => { validate(); compute(); }); els.filingStatus.forEach(r => r.addEventListener('change', () => { validate(); compute(); })); els.calcBtn.addEventListener('click', compute); els.resetBtn.addEventListener('click', () => { $('#fsSingle').checked = true; els.frequency.value = 'biweekly'; els.grossPerPay.value = ''; els.pretaxPerPay.value = ''; els.otherJobsIncome.value = ''; els.otherIncome.value = ''; els.itemized.value = ''; els.kidsU17.value = '0'; els.otherDeps.value = '0'; els.currentWithheld.value = ''; // clear errors [els.freqErr, els.grossErr, els.pretaxErr, els.ojErr, els.oincErr, els.itemErr, els.kidsErr, els.odepsErr, els.cwErr].forEach(e => e.textContent = '');
Formula (extracted text)
Annualize wages and compute AGI: 1) \( W_a = (W_p - P_p)\times n \) 2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \) 3) \( \mathrm{AGI} = W_{\text{total}} + O \) Deduction used: 4) \( D = \max(\mathrm{SD}_f,\, ID) \) 5) \( TI = \max(0,\, \mathrm{AGI} - D) \) Progressive tax (piecewise by filing status f): 6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates. Child & dependent credits with phaseout: 7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \) 8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \) 9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \) 10) \( C = \max(0,\, C_0 - R) \) 11) \( T_{\text{net}} = \max(0,\, T - C) \) Allocate to this job and convert to per‑paycheck: 12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \) 13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
Variables and units
- T = property tax (annual or monthly depending on input) (currency)
- I = homeowners insurance (annual or monthly depending on input) (currency)
Sources (authoritative):
- Direct PDF — irs.gov · Accessed 2026-01-19
https://www.irs.gov/pub/irs-pdf/p15t.pdf - Reference — irs.gov · Accessed 2026-01-19
https://www.irs.gov/forms-pubs/about-publication-505 - Direct PDF — irs.gov · Accessed 2026-01-19
https://www.irs.gov/pub/irs-drop/rp-23-34.pdf - Reference — irs.gov · Accessed 2026-01-19
https://www.irs.gov/forms-pubs/about-form-w-4 - Official tool — irs.gov · Accessed 2026-01-19
https://www.irs.gov/individuals/tax-withholding-estimator
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.
W-4 Withholding Calculator
Quickly estimate your federal income tax withholding per paycheck and generate ready-to-use W‑4 entries (Steps 3 and 4). Ideal for employees, HR, and payroll planners who want accurate, transparent figures without guesswork.
Results
Annual wages from this job
$0.00
Estimated AGI (annual)
$0.00
Deduction used (standard or itemized)
$0.00
Taxable income (annual)
$0.00
Federal tax before credits (annual)
$0.00
Child & dependent credits applied (annual)
$0.00
Estimated federal tax (annual, after credits)
$0.00
Estimated federal withholding needed per paycheck (this job)
$0.00
Suggested W‑4 Step 3 (dependents)
$0.00
Suggested W‑4 Step 4(a) (other income)
$0.00
Suggested W‑4 Step 4(b) (deductions exceeding standard)
$0.00
Suggested W‑4 Step 4(c) Extra withholding per paycheck
$0.00
Note: If you provided your current withholding per paycheck, Step 4(c) suggests the incremental amount to reach the target withholding. Otherwise, it displays the full target withholding per paycheck.
Data Source and Methodology
This estimator uses the IRS annualization approach and 2024 tax parameters:
- IRS Publication 15-T (2024) — Federal Income Tax Withholding Methods. Direct PDF
- IRS Publication 505 (2024) — Tax Withholding and Estimated Tax. Reference
- Revenue Procedure 2023-34 — 2024 inflation adjustments (tax brackets). Direct PDF
- Form W‑4 and Instructions (2024). Reference
- IRS Tax Withholding Estimator. Official tool
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Annualize wages and compute AGI:
1) \( W_a = (W_p - P_p)\times n \)
2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \)
3) \( \mathrm{AGI} = W_{\text{total}} + O \)
Deduction used:
4) \( D = \max(\mathrm{SD}_f,\, ID) \)
5) \( TI = \max(0,\, \mathrm{AGI} - D) \)
Progressive tax (piecewise by filing status f):
6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates.
Child & dependent credits with phaseout:
7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \)
8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \)
9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \)
10) \( C = \max(0,\, C_0 - R) \)
11) \( T_{\text{net}} = \max(0,\, T - C) \)
Allocate to this job and convert to per‑paycheck:
12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \)
13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
1) \( W_a = (W_p - P_p)\times n \)
2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \)
3) \( \mathrm{AGI} = W_{\text{total}} + O \)
Deduction used:
4) \( D = \max(\mathrm{SD}_f,\, ID) \)
5) \( TI = \max(0,\, \mathrm{AGI} - D) \)
Progressive tax (piecewise by filing status f):
6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates.
Child & dependent credits with phaseout:
7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \)
8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \)
9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \)
10) \( C = \max(0,\, C_0 - R) \)
11) \( T_{\text{net}} = \max(0,\, T - C) \)
Allocate to this job and convert to per‑paycheck:
12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \)
13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
Glossary of Variables
- Wp: Gross pay per period for this job
- Pp: Pre-tax deductions per period (401k, HSA, etc.)
- n: Pay periods per year (weekly=52, biweekly=26, semimonthly=24, monthly=12, annually=1)
- Wa: Annual wages from this job after pre-tax deductions
- WotherJobs: Annual wages from other job(s) or spouse
- O: Other annual income (interest, dividends, side work)
- SDf: Standard deduction for filing status f
- ID: Itemized deductions total
- TI: Taxable income
- T: Federal tax before credits
- C: Child and dependent credits after phaseout (nonrefundable portion applied)
- Tnet: Net federal tax after credits
- s: Share of total earned income attributable to this job
- Wpp: Estimated withholding needed per paycheck for this job
How It Works: A Step‑by‑Step Example
Scenario: Filing status Single; Biweekly pay (26/yr); Gross per period $3,000; Pre‑tax $200; No other jobs; No other income; Itemized $0; One child under 17; No other dependents.
- Annualize this job: Wa = (3000 − 200) × 26 = $72,800.
- AGI = Wa + WotherJobs + O = 72,800 + 0 + 0 = $72,800.
- Standard deduction (Single, 2024) SD = $14,600. Itemized = $0 → Use $14,600.
- Taxable income TI = 72,800 − 14,600 = $58,200.
- Tax before credits T (2024 Single brackets): 10% of 11,600 = $1,160; 12% of 35,550 (11,600–47,150) = $4,266; 22% of 11,050 (47,150–58,200) = $2,431; Total T ≈ $7,857.
- Credits: C0 = 1 × $2,000 = $2,000. AGI below $200,000 → no phaseout. C = $2,000.
- Tnet = 7,857 − 2,000 = $5,857.
- Share s = Wa / Wa = 1. Per‑paycheck Wpp = 5,857 / 26 ≈ $225.27.
- W‑4 Suggestions: Step 3 = $2,000; Step 4(a) = $0; Step 4(b) = $0 (no excess over standard); If your current withholding is, say, $180, Step 4(c) ≈ 225.27 − 180 = $45.27.
Frequently Asked Questions (FAQ)
Is this calculator compliant with the 2020+ W‑4 design?
Yes. It reflects the current W‑4 structure (Steps 1–5) and provides suggestions for Steps 3 and 4 based on IRS publications.
How accurate is the per‑paycheck estimate?
It uses annualization aligned with IRS guidance and 2024 brackets. Actual payroll systems follow IRS tables, so small differences can occur. Entering other jobs’ wages improves accuracy.
Do you handle the Child Tax Credit phaseout?
Yes. We apply the $50 per $1,000 (or fraction) reduction above $200,000 (Single/HOH) or $400,000 (MFJ), and cap the nonrefundable credit at your tax.
What do I put on Step 4(b)?
Only the amount by which your itemized deductions exceed the standard deduction for your filing status. The calculator shows this value directly.
Where can I verify official figures?
See IRS Publication 15‑T, Publication 505, and the IRS Tax Withholding Estimator linked above. You can also review the W‑4 instructions.
Is this tax advice?
No. This tool is for educational planning. Consult a tax professional for advice about your specific situation.
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[','\]
','
Formula (extracted LaTeX)
\[= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); const money = (n) => new Intl.NumberFormat('en-US', { style:'currency', currency:'USD', maximumFractionDigits:2 }).format(Number.isFinite(n)? n : 0); const clampNonNeg = (v) => isNaN(v)||v<0 ? 0 : v; // Elements const els = { filingStatus:\]
= (sel, ctx=document) => Array.from(ctx.querySelectorAll(sel)); const money = (n) => new Intl.NumberFormat('en-US', { style:'currency', currency:'USD', maximumFractionDigits:2 }).format(Number.isFinite(n)? n : 0); const clampNonNeg = (v) => isNaN(v)||v<0 ? 0 : v; // Elements const els = { filingStatus:
Formula (extracted LaTeX)
\[('.tooltip-btn').forEach(btn => { btn.addEventListener('click', () => { const id = btn.getAttribute('aria-controls'); const panel = document.getElementById(id); const expanded = btn.getAttribute('aria-expanded') === 'true'; btn.setAttribute('aria-expanded', String(!expanded)); panel.setAttribute('aria-hidden', String(expanded)); }); btn.addEventListener('keydown', (e) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); btn.click(); } }); }); // Parameters (2024) const STANDARD_DEDUCTION = { single: 14600, mfj: 29200, hoh: 21900 }; const BRACKETS_2024 = { single: [ [0, 11600, 0.10], [11600, 47150, 0.12], [47150, 100525, 0.22], [100525, 191950, 0.24], [191950, 243725, 0.32], [243725, 609350, 0.35], [609350, Infinity, 0.37] ], mfj: [ [0, 23200, 0.10], [23200, 94300, 0.12], [94300, 201050, 0.22], [201050, 383900, 0.24], [383900, 487450, 0.32], [487450, 731200, 0.35], [731200, Infinity, 0.37] ], hoh: [ [0, 16550, 0.10], [16550, 63100, 0.12], [63100, 100500, 0.22], [100500, 191950, 0.24], [191950, 243700, 0.32], [243700, 609350, 0.35], [609350, Infinity, 0.37] ] }; const CTC_PHASEOUT = { single:200000, hoh:200000, mfj:400000 }; const PERIODS = { weekly: 52, biweekly: 26, semimonthly: 24, monthly: 12, annually: 1 }; function getFilingStatus() { const checked = els.filingStatus.find(r => r.checked); return checked ? checked.value : 'single'; } function getPeriods() { return PERIODS[els.frequency.value] || 26; } // Validation function setError(input, errEl, message) { if (!errEl) return; if (message) { input?.setAttribute('aria-invalid', 'true'); errEl.textContent = message; } else { input?.setAttribute('aria-invalid', 'false'); errEl.textContent = ''; } } function validate() { let ok = true; // frequency if (!PERIODS.hasOwnProperty(els.frequency.value)) { setError(els.frequency, els.freqErr, 'Please choose a valid pay frequency.'); ok = false; } else { setError(els.frequency, els.freqErr, ''); } // gross const gross = parseFloat(els.grossPerPay.value); if (isNaN(gross) || gross <= 0) { setError(els.grossPerPay, els.grossErr, 'Enter a positive gross pay per period (e.g., 3000).'); ok = false; } else { setError(els.grossPerPay, els.grossErr, ''); } // pretax not exceeding gross const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); if (!isNaN(gross) && pretax > gross) { setError(els.pretaxPerPay, els.pretaxErr, 'Pre-tax deductions cannot exceed your gross pay.'); ok = false; } else { setError(els.pretaxPerPay, els.pretaxErr, ''); } // integers for dependents const kids = Number(els.kidsU17.value); const odep = Number(els.otherDeps.value); if (!Number.isInteger(kids) || kids < 0) { setError(els.kidsU17, els.kidsErr, 'Enter a whole number of children under 17 (0 or more).'); ok = false; } else setError(els.kidsU17, els.kidsErr, ''); if (!Number.isInteger(odep) || odep < 0) { setError(els.otherDeps, els.odepsErr, 'Enter a whole number of other dependents (0 or more).'); ok = false; } else setError(els.otherDeps, els.odepsErr, ''); // other numeric fields sanity const fields = [ [els.otherJobsIncome, els.ojErr, 'Enter a non-negative annual amount or leave blank.'], [els.otherIncome, els.oincErr, 'Enter a non-negative annual amount or leave blank.'], [els.itemized, els.itemErr, 'Enter a non-negative annual amount or leave blank.'], [els.currentWithheld, els.cwErr, 'Enter a non-negative amount or leave blank.'] ]; for (const [input, err, msg] of fields) { const val = parseFloat(input.value); if (input.value !== '' && (isNaN(val) || val < 0)) { setError(input, err, msg); ok = false; } else { setError(input, err, ''); } } return ok; } function taxFromBrackets(fstatus, taxable) { const brackets = BRACKETS_2024[fstatus] || BRACKETS_2024.single; let tax = 0; let remaining = taxable; if (remaining <= 0) return 0; for (const [l,u,r] of brackets) { if (remaining <= 0) break; const lower = l; const upper = Math.min(u, taxable); if (upper > lower) { const slice = upper - lower; tax += slice * r; } } return tax; } function compute() { if (!validate()) return; const fstatus = getFilingStatus(); const periods = getPeriods(); const gross = clampNonNeg(parseFloat(els.grossPerPay.value)); const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); const otherJobs = clampNonNeg(parseFloat(els.otherJobsIncome.value)); const otherInc = clampNonNeg(parseFloat(els.otherIncome.value)); const itemized = clampNonNeg(parseFloat(els.itemized.value)); const kids = clampNonNeg(parseFloat(els.kidsU17.value)); const odep = clampNonNeg(parseFloat(els.otherDeps.value)); const currentWithheld = clampNonNeg(parseFloat(els.currentWithheld.value)); const taxablePerPay = Math.max(0, gross - pretax); const annualThisJob = taxablePerPay * periods; const totalEarned = annualThisJob + otherJobs; const AGI = totalEarned + otherInc; const stdDed = STANDARD_DEDUCTION[fstatus] || STANDARD_DEDUCTION.single; const deductionUsed = Math.max(stdDed, itemized); const taxableIncome = Math.max(0, AGI - deductionUsed); const taxBefore = taxFromBrackets(fstatus, taxableIncome); // Credits const baseCredit = 2000 * Math.round(kids) + 500 * Math.round(odep); const phaseThr = CTC_PHASEOUT[fstatus] || 200000; const excess = Math.max(0, AGI - phaseThr); const reduction = excess > 0 ? 50 * Math.ceil(excess / 1000) : 0; const creditAfterPhase = Math.max(0, baseCredit - reduction); const creditApplied = Math.min(creditAfterPhase, taxBefore); const taxAfter = Math.max(0, taxBefore - creditApplied); // Allocation to this job const share = totalEarned > 0 ? (annualThisJob / totalEarned) : 1; const perPayNeeded = (taxAfter * share) / Math.max(1, periods); // W-4 suggestions const step3 = baseCredit; // Amount entered on Step 3 equals estimated nonrefundable credits total const step4a = otherInc; // as entered const step4b = Math.max(0, itemized - stdDed); // excess over standard let step4c; // per paycheck extra withholding if (currentWithheld > 0) { step4c = Math.max(0, perPayNeeded - currentWithheld); } else { // If user doesn't know current withholding, show full target per-pay withholding as a conservative guide step4c = perPayNeeded; } // Update UI els.resAnnualThis.textContent = money(annualThisJob); els.resAGI.textContent = money(AGI); els.resDeductionUsed.textContent = money(deductionUsed); els.resTaxable.textContent = money(taxableIncome); els.resTaxBefore.textContent = money(taxBefore); els.resCredits.textContent = money(creditApplied); els.resTaxAfter.textContent = money(taxAfter); els.resPerPay.textContent = money(perPayNeeded); els.resStep3.textContent = money(step3); els.resStep4a.textContent = money(step4a); els.resStep4b.textContent = money(step4b); els.resStep4c.textContent = money(step4c); } // Events ['blur','change','input'].forEach(ev => { els.grossPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.pretaxPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherJobsIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.itemized.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.kidsU17.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherDeps.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.currentWithheld.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); }); els.frequency.addEventListener('change', () => { validate(); compute(); }); els.filingStatus.forEach(r => r.addEventListener('change', () => { validate(); compute(); })); els.calcBtn.addEventListener('click', compute); els.resetBtn.addEventListener('click', () => { $('#fsSingle').checked = true; els.frequency.value = 'biweekly'; els.grossPerPay.value = ''; els.pretaxPerPay.value = ''; els.otherJobsIncome.value = ''; els.otherIncome.value = ''; els.itemized.value = ''; els.kidsU17.value = '0'; els.otherDeps.value = '0'; els.currentWithheld.value = ''; // clear errors [els.freqErr, els.grossErr, els.pretaxErr, els.ojErr, els.oincErr, els.itemErr, els.kidsErr, els.odepsErr, els.cwErr].forEach(e => e.textContent = '');\]
('.tooltip-btn').forEach(btn => { btn.addEventListener('click', () => { const id = btn.getAttribute('aria-controls'); const panel = document.getElementById(id); const expanded = btn.getAttribute('aria-expanded') === 'true'; btn.setAttribute('aria-expanded', String(!expanded)); panel.setAttribute('aria-hidden', String(expanded)); }); btn.addEventListener('keydown', (e) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); btn.click(); } }); }); // Parameters (2024) const STANDARD_DEDUCTION = { single: 14600, mfj: 29200, hoh: 21900 }; const BRACKETS_2024 = { single: [ [0, 11600, 0.10], [11600, 47150, 0.12], [47150, 100525, 0.22], [100525, 191950, 0.24], [191950, 243725, 0.32], [243725, 609350, 0.35], [609350, Infinity, 0.37] ], mfj: [ [0, 23200, 0.10], [23200, 94300, 0.12], [94300, 201050, 0.22], [201050, 383900, 0.24], [383900, 487450, 0.32], [487450, 731200, 0.35], [731200, Infinity, 0.37] ], hoh: [ [0, 16550, 0.10], [16550, 63100, 0.12], [63100, 100500, 0.22], [100500, 191950, 0.24], [191950, 243700, 0.32], [243700, 609350, 0.35], [609350, Infinity, 0.37] ] }; const CTC_PHASEOUT = { single:200000, hoh:200000, mfj:400000 }; const PERIODS = { weekly: 52, biweekly: 26, semimonthly: 24, monthly: 12, annually: 1 }; function getFilingStatus() { const checked = els.filingStatus.find(r => r.checked); return checked ? checked.value : 'single'; } function getPeriods() { return PERIODS[els.frequency.value] || 26; } // Validation function setError(input, errEl, message) { if (!errEl) return; if (message) { input?.setAttribute('aria-invalid', 'true'); errEl.textContent = message; } else { input?.setAttribute('aria-invalid', 'false'); errEl.textContent = ''; } } function validate() { let ok = true; // frequency if (!PERIODS.hasOwnProperty(els.frequency.value)) { setError(els.frequency, els.freqErr, 'Please choose a valid pay frequency.'); ok = false; } else { setError(els.frequency, els.freqErr, ''); } // gross const gross = parseFloat(els.grossPerPay.value); if (isNaN(gross) || gross <= 0) { setError(els.grossPerPay, els.grossErr, 'Enter a positive gross pay per period (e.g., 3000).'); ok = false; } else { setError(els.grossPerPay, els.grossErr, ''); } // pretax not exceeding gross const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); if (!isNaN(gross) && pretax > gross) { setError(els.pretaxPerPay, els.pretaxErr, 'Pre-tax deductions cannot exceed your gross pay.'); ok = false; } else { setError(els.pretaxPerPay, els.pretaxErr, ''); } // integers for dependents const kids = Number(els.kidsU17.value); const odep = Number(els.otherDeps.value); if (!Number.isInteger(kids) || kids < 0) { setError(els.kidsU17, els.kidsErr, 'Enter a whole number of children under 17 (0 or more).'); ok = false; } else setError(els.kidsU17, els.kidsErr, ''); if (!Number.isInteger(odep) || odep < 0) { setError(els.otherDeps, els.odepsErr, 'Enter a whole number of other dependents (0 or more).'); ok = false; } else setError(els.otherDeps, els.odepsErr, ''); // other numeric fields sanity const fields = [ [els.otherJobsIncome, els.ojErr, 'Enter a non-negative annual amount or leave blank.'], [els.otherIncome, els.oincErr, 'Enter a non-negative annual amount or leave blank.'], [els.itemized, els.itemErr, 'Enter a non-negative annual amount or leave blank.'], [els.currentWithheld, els.cwErr, 'Enter a non-negative amount or leave blank.'] ]; for (const [input, err, msg] of fields) { const val = parseFloat(input.value); if (input.value !== '' && (isNaN(val) || val < 0)) { setError(input, err, msg); ok = false; } else { setError(input, err, ''); } } return ok; } function taxFromBrackets(fstatus, taxable) { const brackets = BRACKETS_2024[fstatus] || BRACKETS_2024.single; let tax = 0; let remaining = taxable; if (remaining <= 0) return 0; for (const [l,u,r] of brackets) { if (remaining <= 0) break; const lower = l; const upper = Math.min(u, taxable); if (upper > lower) { const slice = upper - lower; tax += slice * r; } } return tax; } function compute() { if (!validate()) return; const fstatus = getFilingStatus(); const periods = getPeriods(); const gross = clampNonNeg(parseFloat(els.grossPerPay.value)); const pretax = clampNonNeg(parseFloat(els.pretaxPerPay.value)); const otherJobs = clampNonNeg(parseFloat(els.otherJobsIncome.value)); const otherInc = clampNonNeg(parseFloat(els.otherIncome.value)); const itemized = clampNonNeg(parseFloat(els.itemized.value)); const kids = clampNonNeg(parseFloat(els.kidsU17.value)); const odep = clampNonNeg(parseFloat(els.otherDeps.value)); const currentWithheld = clampNonNeg(parseFloat(els.currentWithheld.value)); const taxablePerPay = Math.max(0, gross - pretax); const annualThisJob = taxablePerPay * periods; const totalEarned = annualThisJob + otherJobs; const AGI = totalEarned + otherInc; const stdDed = STANDARD_DEDUCTION[fstatus] || STANDARD_DEDUCTION.single; const deductionUsed = Math.max(stdDed, itemized); const taxableIncome = Math.max(0, AGI - deductionUsed); const taxBefore = taxFromBrackets(fstatus, taxableIncome); // Credits const baseCredit = 2000 * Math.round(kids) + 500 * Math.round(odep); const phaseThr = CTC_PHASEOUT[fstatus] || 200000; const excess = Math.max(0, AGI - phaseThr); const reduction = excess > 0 ? 50 * Math.ceil(excess / 1000) : 0; const creditAfterPhase = Math.max(0, baseCredit - reduction); const creditApplied = Math.min(creditAfterPhase, taxBefore); const taxAfter = Math.max(0, taxBefore - creditApplied); // Allocation to this job const share = totalEarned > 0 ? (annualThisJob / totalEarned) : 1; const perPayNeeded = (taxAfter * share) / Math.max(1, periods); // W-4 suggestions const step3 = baseCredit; // Amount entered on Step 3 equals estimated nonrefundable credits total const step4a = otherInc; // as entered const step4b = Math.max(0, itemized - stdDed); // excess over standard let step4c; // per paycheck extra withholding if (currentWithheld > 0) { step4c = Math.max(0, perPayNeeded - currentWithheld); } else { // If user doesn't know current withholding, show full target per-pay withholding as a conservative guide step4c = perPayNeeded; } // Update UI els.resAnnualThis.textContent = money(annualThisJob); els.resAGI.textContent = money(AGI); els.resDeductionUsed.textContent = money(deductionUsed); els.resTaxable.textContent = money(taxableIncome); els.resTaxBefore.textContent = money(taxBefore); els.resCredits.textContent = money(creditApplied); els.resTaxAfter.textContent = money(taxAfter); els.resPerPay.textContent = money(perPayNeeded); els.resStep3.textContent = money(step3); els.resStep4a.textContent = money(step4a); els.resStep4b.textContent = money(step4b); els.resStep4c.textContent = money(step4c); } // Events ['blur','change','input'].forEach(ev => { els.grossPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.pretaxPerPay.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherJobsIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherIncome.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.itemized.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.kidsU17.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.otherDeps.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); els.currentWithheld.addEventListener(ev, () => { if (ev==='blur' || ev==='change') validate(); compute(); }); }); els.frequency.addEventListener('change', () => { validate(); compute(); }); els.filingStatus.forEach(r => r.addEventListener('change', () => { validate(); compute(); })); els.calcBtn.addEventListener('click', compute); els.resetBtn.addEventListener('click', () => { $('#fsSingle').checked = true; els.frequency.value = 'biweekly'; els.grossPerPay.value = ''; els.pretaxPerPay.value = ''; els.otherJobsIncome.value = ''; els.otherIncome.value = ''; els.itemized.value = ''; els.kidsU17.value = '0'; els.otherDeps.value = '0'; els.currentWithheld.value = ''; // clear errors [els.freqErr, els.grossErr, els.pretaxErr, els.ojErr, els.oincErr, els.itemErr, els.kidsErr, els.odepsErr, els.cwErr].forEach(e => e.textContent = '');
Formula (extracted text)
Annualize wages and compute AGI: 1) \( W_a = (W_p - P_p)\times n \) 2) \( W_{\text{total}} = W_a + W_{\text{otherJobs}} \) 3) \( \mathrm{AGI} = W_{\text{total}} + O \) Deduction used: 4) \( D = \max(\mathrm{SD}_f,\, ID) \) 5) \( TI = \max(0,\, \mathrm{AGI} - D) \) Progressive tax (piecewise by filing status f): 6) \( T = \sum_{i} r_i \cdot \max\big(0,\, \min(TI,\, u_i) - l_i\big) \), where \([l_i,u_i)\) are bracket bounds and \(r_i\) the rates. Child & dependent credits with phaseout: 7) \( C_0 = 2000 \cdot N_{<17} + 500 \cdot N_{\text{other}} \) 8) \( \text{Thr}_f = \begin{cases} 400{,}000 & f=\text{MFJ}\\ 200{,}000 & f\in\{\text{Single},\text{HOH}\} \end{cases} \) 9) \( R = 50 \cdot \left\lceil \dfrac{\max(0,\, \mathrm{AGI}-\text{Thr}_f)}{1000} \right\rceil \) 10) \( C = \max(0,\, C_0 - R) \) 11) \( T_{\text{net}} = \max(0,\, T - C) \) Allocate to this job and convert to per‑paycheck: 12) \( s = \dfrac{W_a}{\max(W_{\text{total}},1)} \) 13) \( W_{\text{pp}} = \dfrac{T_{\text{net}}\cdot s}{n} \)
Variables and units
- T = property tax (annual or monthly depending on input) (currency)
- I = homeowners insurance (annual or monthly depending on input) (currency)
Sources (authoritative):
- Direct PDF — irs.gov · Accessed 2026-01-19
https://www.irs.gov/pub/irs-pdf/p15t.pdf - Reference — irs.gov · Accessed 2026-01-19
https://www.irs.gov/forms-pubs/about-publication-505 - Direct PDF — irs.gov · Accessed 2026-01-19
https://www.irs.gov/pub/irs-drop/rp-23-34.pdf - Reference — irs.gov · Accessed 2026-01-19
https://www.irs.gov/forms-pubs/about-form-w-4 - Official tool — irs.gov · Accessed 2026-01-19
https://www.irs.gov/individuals/tax-withholding-estimator
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.