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Biweekly Mortgage Calculator

Pay biweekly and slash years of mortgage interest

How it is calculated

First the tool finds the ordinary monthly payment with the standard formula M = P × i ÷ (1 − (1 + i)−n), where i = rate ÷ 100 ÷ 12 and n = years × 12 (at 0% it is P ÷ n). Total monthly-plan interest is M × n − P.

Then it simulates the biweekly plan: a payment of M ÷ 2 every two weeks, with interest each period of balance × rate ÷ 100 ÷ 26, until the balance reaches zero. Periods are converted to months with periods × 12 ÷ 26. Months saved are the original term minus that figure, rounded, and interest saved is the difference in total interest. Since 26 half-payments equal 13 monthly payments, you pay one extra month's payment a year. The tool assumes the lender applies each payment immediately; plans that hold half-payments until a full month is collected save less.

Worked example

A 250000 loan at 6.5% for 30 years.

Monthly payment: i = 0.065 ÷ 12, n = 360, giving M ≈ 1580.17, so total interest over 30 years is 1580.17 × 360 − 250000 ≈ 318,861. Biweekly payment: 1580.17 ÷ 2 = $790.09. The simulation clears the loan in 628 biweekly periods, about 289.8 months, with roughly 245,426 of interest. That saves 360 − 289.8, or 70 months, and about $73,435 of interest.

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Common mistakes

  • Confusing biweekly (every two weeks, 26 payments a year) with twice a month (24 payments a year). Twice a month gives no extra payment, so the savings do not apply.
  • Assuming every lender applies biweekly payments right away. Some hold each half-payment until the full monthly amount is available, which removes most of the benefit.
  • Ignoring fees. Some lenders charge for a biweekly service, which can eat into the interest saved.
  • Entering the balance of an older loan with its original term. Use the current balance and the remaining years.
  • Expecting the result for an escrow payment. Only principal and interest are modelled, not taxes and insurance.

Sources

About this calculator

This calculator compares a standard monthly mortgage schedule against paying half the monthly payment every two weeks instead. Because a year has slightly more than 52 weeks, this pattern quietly results in the equivalent of one extra full monthly payment per year, which shortens the loan term and reduces total interest paid without requiring a large lump sum.

Homeowners use it to see the concrete effect of switching payment frequency, both in terms of years shaved off the mortgage and dollars saved on interest, before committing to a biweekly plan through their lender. It's a common comparison for anyone looking for a low-effort way to pay off a mortgage faster.

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  • Editorial team

    Before trusting the saving here, ask whether the lender applies each half payment on the day it arrives. Some hold the first half until the second one comes in, which wipes out most of the benefit, and third-party biweekly programs may charge setup fees that this result leaves out. The same effect can usually be had by adding one twelfth of the monthly payment to every monthly payment. Has your lender offered you a biweekly plan, and on what terms?

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