Biweekly Mortgage Payment Calculator

Calculate your potential savings with a biweekly mortgage payment plan using our advanced calculator tool.

Loan Details

Full original guide (expanded)

This calculator helps homeowners determine potential savings when switching from monthly to biweekly mortgage payments.

Biweekly mortgage payments involve making a half-payment every two weeks, resulting in 26 half-payments per year, or 13 full payments.

Biweekly payments reduce the loan balance faster, decreasing the interest paid over the life of the loan.

Data Source and Methodology

The calculations are based on standard mortgage amortization formulas. Consult your financial advisor for personalized advice.

Glossary of Terms

  • Loan Amount: Total amount of the mortgage.
  • Interest Rate: Annual interest rate charged on the loan.
  • Loan Term: Duration over which the loan is repaid.

Frequently Asked Questions (FAQ)

What is a biweekly mortgage payment?

Biweekly mortgage payments involve making a half-payment every two weeks, resulting in 26 half-payments per year, or 13 full payments.

How can biweekly payments save money?

Biweekly payments reduce the loan balance faster, decreasing the interest paid over the life of the loan.

Formulas

Biweekly Payment (principal + interest):

P = [r × A / (1 - (1 + r)-n)] / 2

  • P: Principal (loan amount)
  • r: Periodic interest rate (annual rate ÷ 26)
  • n: Total number of biweekly payments (years × 26)
Citations

CFPB explainer: Mortgage payment calculation

CFPB consumer education: Mortgages consumer tools

Federal Reserve consumer resources: Consumer & community resources

Changelog
  • v0.1.0-draft — Initial audit spec draft generated from HTML extraction (review required).
  • v0.1.0-draft — Verify formulas match the calculator engine and convert text-only formulas to LaTeX.
  • v0.1.0-draft — Confirm sources are authoritative and relevant to the calculator methodology.
✓ Verified by Ugo Candido Last Updated: 2026-01-19 Version 0.1.0-draft
Version 1.5.0
+ round2(safe).toFixed(2); } }; function compute({ principal, annualRatePct, years }) { const paymentsPerYear = 26; const periods = Math.floor(years) * paymentsPerYear; if (!(principal > 0) || !(periods > 0) || !Number.isFinite(annualRatePct)) { return null; } const rate = annualRatePct / 100 / paymentsPerYear; let payment = 0; if (rate === 0) { payment = principal / periods; } else { const pow = Math.pow(1 + rate, periods); payment = (principal * rate * pow) / (pow - 1); } if (!Number.isFinite(payment) || payment <= 0) return null; let balance = principal; let totalInterest = 0; const schedule = []; const MAX_ROWS = periods + 50; for (let i = 1; i <= MAX_ROWS; i++) { if (balance <= 0.005) break; const interest = balance * rate; const principalPaid = payment - interest; if (principalPaid < 0) break; const actualPrincipal = Math.min(principalPaid, balance); balance = balance - actualPrincipal; totalInterest += interest; schedule.push({ num: i, total: round2(payment), int: round2(interest), prin: round2(actualPrincipal), bal: round2(Math.max(0, balance)) }); } return { paymentPerPeriod: payment, totalInterest: round2(totalInterest), schedule, periods }; } const els = { loanAmount: document.getElementById('loanAmount'), interestRate: document.getElementById('interestRate'), loanTerm: document.getElementById('loanTerm'), biweeklyPayment: document.getElementById('biweeklyPayment'), interestSaved: document.getElementById('interestSaved'), loanPaidOffIn: document.getElementById('loanPaidOffIn'), errorBox: document.getElementById('errorBox'), scheduleWrap: document.getElementById('scheduleWrap'), scheduleBody: document.getElementById('scheduleBody'), toggleSchedule: document.getElementById('toggleSchedule'), downloadCsv: document.getElementById('downloadCsv'), calcBtn: document.getElementById('calcBtn'), resetBtn: document.getElementById('resetBtn') }; let currentSchedule = []; function parseInputs() { const yearsRaw = Number(els.loanTerm.value); return { principal: Number(els.loanAmount.value), annualRatePct: Number(els.interestRate.value), years: Number.isFinite(yearsRaw) ? Math.floor(Math.max(0, yearsRaw)) : 0 }; } function validate(inputs) { const errors = []; if (!Number.isFinite(inputs.principal) || inputs.principal <= 0) { errors.push('Loan amount must be greater than 0.'); } if (!Number.isFinite(inputs.years) || inputs.years <= 0) { errors.push('Loan term (years) must be greater than 0.'); } if (!Number.isFinite(inputs.annualRatePct) || inputs.annualRatePct < 0) { errors.push('Interest rate must be 0 or greater.'); } return { ok: errors.length === 0, errors }; } function format(calc, inputs) { const years = Math.floor(calc.periods / 26); const biweeklyPayment = fmtCurrency(round2(calc.paymentPerPeriod)); const totalInterest = calc.totalInterest; const interestSaved = fmtCurrency(round2((inputs.principal * (inputs.annualRatePct / 100 / 26) * calc.periods / 26) - totalInterest)); return { biweeklyPayment, interestSaved, loanPaidOffIn: `${years} years`, totalInterest: fmtCurrency(totalInterest) }; } function render(formatted, errors) { if (!errors.length) { els.errorBox.style.display = 'none'; els.errorBox.textContent = ''; } else { els.errorBox.style.display = 'block'; els.errorBox.textContent = errors.join(' '); } if (formatted) { els.biweeklyPayment.textContent = formatted.biweeklyPayment; els.interestSaved.textContent = formatted.interestSaved; els.loanPaidOffIn.textContent = formatted.loanPaidOffIn; } } function renderTable() { els.scheduleBody.innerHTML = ''; const rows = currentSchedule.slice(0, 360); const frag = document.createDocumentFragment(); for (const row of rows) { const tr = document.createElement('tr'); tr.innerHTML = ` ${row.num} ${fmtCurrency(row.total)} ${fmtCurrency(row.int)} ${fmtCurrency(row.prin)} ${fmtCurrency(row.bal)} `; frag.appendChild(tr); } els.scheduleBody.appendChild(frag); } function update() { const inputs = parseInputs(); const validation = validate(inputs); if (!validation.ok) { render(null, validation.errors); els.downloadCsv.disabled = true; return; } const calc = compute(inputs); if (!calc) { render(null, ['Calculation failed for the current inputs. Please revise values.']); els.downloadCsv.disabled = true; return; } currentSchedule = calc.schedule; const formatted = format(calc, inputs); render(formatted, []); els.downloadCsv.disabled = currentSchedule.length === 0; if (els.scheduleWrap.style.display === 'block') { renderTable(); } } function resetForm() { els.loanAmount.value = '250000'; els.interestRate.value = '3.5'; els.loanTerm.value = '30'; const debouncedUpdate = debounce(update, 100); document.querySelectorAll('#inputsCard input, #inputsCard select, #inputsCard textarea') .forEach((el) => { el.addEventListener('input', debouncedUpdate); el.addEventListener('change', debouncedUpdate); }); update(); } function debounce(fn, delay = 100) { let timeout; return (...args) => { clearTimeout(timeout); timeout = setTimeout(() => fn(...args), delay); }; } els.calcBtn.addEventListener('click', update); els.resetBtn.addEventListener('click', resetForm); els.toggleSchedule.addEventListener('click', () => { const show = els.scheduleWrap.style.display !== 'block'; els.scheduleWrap.style.display = show ? 'block' : 'none'; els.toggleSchedule.textContent = show ? 'Hide Amortization Schedule' : 'View Amortization Schedule'; if (show) { renderTable(); } }); els.downloadCsv.addEventListener('click', () => { if (currentSchedule.length === 0) return; let csv = '#,Total Payment,Interest,Principal,Balance\n'; for (const row of currentSchedule) { csv += `${row.num},${row.total},${row.int},${row.prin},${row.bal}\n`; } const blob = new Blob([csv], { type: 'text/csv' }); const url = URL.createObjectURL(blob); const a = document.createElement('a'); a.href = url; a.download = 'amortization-schedule.csv'; a.click(); URL.revokeObjectURL(url); }); el.addEventListener('change', debouncedUpdate); }); update(); })();