Payroll Calculator

Compute take-home pay with federal withholding, Social Security, Medicare (including the 0.9% Additional Medicare tax), plus custom state and local taxes. Supports pre-tax and post-tax deductions.

Full original guide (expanded)

Data source & methodology

Federal payroll taxes are based on IRS employer guidance. Social Security (OASDI) and Medicare (HI) rates and the annual wage base follow IRS Publication 15 (Circular E) — 2025 and the SSA Contribution and Benefit Base (2025 wage base $176,100). The 0.9% Additional Medicare withholding applies after $200,000 of wages from a single employer (see IRS Topic No. 560 and Q&A). All references current to 2025.
“Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.”

The formulas, explained

Gross (period): \( \; G = \begin{cases} h \times r & \text{(hourly)} \\ s & \text{(salary per period)} \end{cases} \)

Taxable wages for income tax (approximate with pre-tax deductions \(D_{pre}\)):
\( \; W_{income} = \max(0, G - D_{pre}) \)

Social Security (6.2%), up to annual base \(B\):
\( \; SS = 0.062 \times \min(B - \text{YTD}_{SS}, \; \max(0, G - D_{pre})) \)

Medicare (1.45%): \( \; M = 0.0145 \times \max(0, G - D_{pre}) \)

Additional Medicare (0.9%) when employer wages exceed \$200{,}000 YTD:
\( \; AM = 0.009 \times \max\big(0,\; \text{YTD} + (G - D_{pre}) - 200{,}000\big)_{\text{this period portion}} \)

Federal withholding (effective method): \( \; F = r_f \times W_{income} \)   where \(r_f\) is your chosen effective rate.

State/local: \( \; S = r_s \times W_{income}, \quad L = r_l \times W_{income} \)

Net pay: \( \; \text{Net} = G - D_{pre} - (F + SS + M + AM + S + L) - D_{post} \)

Glossary of inputs & outputs

  • Pay Basis: Hourly (hours × rate) or Salary (amount per pay period).
  • Pay Frequency: Weekly (52), Biweekly (26), Semimonthly (24), Monthly (12).
  • Pre-tax deductions: Amounts excluded before tax (e.g., 401(k), HSA, Section 125 premiums).
  • Post-tax deductions: Deductions after tax (e.g., Roth contributions, garnishments).
  • Federal effective rate: Quick estimate for withholding (% of taxable wages).
  • State/Local: Flat rates applied to taxable wages (user-provided; rules vary by jurisdiction).
  • Net Pay: Take-home (deposit) after all deductions and taxes.

How it works: a step-by-step example

Scenario: Monthly salary of \$5,000; pre-tax \$300 (401(k)); post-tax \$50; federal effective rate 12%; state 4%; local 1%; YTD wages \$0.

  1. Gross \(G = \$5{,}000\). Pre-tax \(D_{pre}=\$300\) → taxable wages \(W_{income}=\$4{,}700\).
  2. FICA: Social Security \(= 6.2\%\times \$4{,}700 = \$291.40\) (assuming under wage base); Medicare \(= 1.45\%\times \$4{,}700 = \$68.15\); Additional Medicare \(= \$0\) (YTD < \$200k).
  3. Federal \(= 12\%\times \$4{,}700 = \$564.00\); State \(= 4\%\times \$4{,}700 = \$188.00\); Local \(= 1\%\times \$4{,}700 = \$47.00\).
  4. Net \(= G - D_{pre} - (\text{taxes}) - D_{post}\) = \( \$5{,}000 - 300 - (291.40 + 68.15 + 0 + 564 + 188 + 47) - 50 \approx \$3{,}491.45\).

FAQ

Does this replace my payroll provider’s exact withholding?

No. This is an estimation tool. Exact withholding uses IRS Pub. 15-T methods plus jurisdiction-specific rules. Use this to sanity-check stubs and model scenarios.

Why use an “effective rate” for federal withholding?

Pub. 15-T methods are complex (W-4 steps, credits, brackets, frequency). An effective rate yields fast, defensible estimates. If you know your per-period federal withholding, choose the “custom” option.

Are pre-tax benefits always excluded from FICA?

Not always. Section 125 health premiums generally reduce FICA; 401(k) reduces income tax but not Social Security/Medicare. Confirm plan rules with HR/payroll.

When does the 0.9% Additional Medicare apply?

Employers must withhold once wages paid by that employer exceed $200,000 in a calendar year (filing status doesn’t matter for employer withholding).

How are state and local taxes handled?

They vary widely. Enter flat rates or \$0 if your state/locality has no income tax, or if your payroll provider handles variable rules.

Can I export results?

Use your browser’s Print to PDF for a clean one-page summary of the results and line items.

Last accuracy review:

Audit: Complete
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted text)
Gross (period): \( \; G = \begin{cases} h \times r & \text{(hourly)} \\ s & \text{(salary per period)} \end{cases} \) Taxable wages for income tax (approximate with pre-tax deductions \(D_{pre}\)): \( \; W_{income} = \max(0, G - D_{pre}) \) Social Security (6.2%), up to annual base \(B\): \( \; SS = 0.062 \times \min(B - \text{YTD}_{SS}, \; \max(0, G - D_{pre})) \) Medicare (1.45%): \( \; M = 0.0145 \times \max(0, G - D_{pre}) \) Additional Medicare (0.9%) when employer wages exceed \$200{,}000 YTD: \( \; AM = 0.009 \times \max\big(0,\; \text{YTD} + (G - D_{pre}) - 200{,}000\big)_{\text{this period portion}} \) Federal withholding (effective method): \( \; F = r_f \times W_{income} \) where \(r_f\) is your chosen effective rate. State/local: \( \; S = r_s \times W_{income}, \quad L = r_l \times W_{income} \) Net pay: \( \; \text{Net} = G - D_{pre} - (F + SS + M + AM + S + L) - D_{post} \)
Variables and units
  • T = property tax (annual or monthly depending on input) (currency)
Sources (authoritative):
Changelog
Version: 0.1.0-draft
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.
Verified by Ugo Candido on 2026-01-19
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Version 0.1.0-draft
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Changelog
  • 0.1.0-draft — 2026-01-19: Initial draft (review required).