Extra Mortgage Payment & Biweekly Calculator

Paying a mortgage off early doesn't require refinancing or a windfall. A modest, consistent extra payment toward principal each month can cut years off a 30-year loan and save tens of thousands in interest, because every extra dollar reduces the balance interest is charged on for the rest of the loan's life. This calculator compares two common ways to do it: a fixed extra amount added to your normal monthly payment, or switching to a biweekly payment schedule.

Biweekly payments work by paying half your normal monthly payment every two weeks instead of the full payment once a month. Since there are 52 weeks in a year, that works out to 26 half-payments: the equivalent of 13 full monthly payments instead of 12, so you make one extra full payment a year without having to consciously budget for it.

How does this calculator work?

Enter your loan amount, interest rate, and term, then choose a strategy: biweekly payments, or a fixed extra dollar amount added to every monthly payment.

The calculator builds two side-by-side amortization schedules, a standard one at your normal payment and an accelerated one under your chosen strategy, using the same amortization engine behind this site's other mortgage calculators, so extra principal payments are applied consistently.

It shows the interest saved, the time saved, and lets you compare the declining balance under both schedules year by year, or drill into the full monthly schedule.

Worked example

A $350,000 mortgage at 6.75% over 30 years, compared under biweekly payments versus an extra $200 paid every month.

Standard monthly payment

$2,270

Biweekly: effective extra per month

≈$189

Biweekly: interest saved

$110,411

Biweekly: payoff

24.0 years (72 months early)

Extra $200/mo: interest saved

$114,979

Extra $200/mo: payoff

23.75 years (75 months early)

How the numbers work

Biweekly payments work out to about $189 in extra principal per month on average, a bit less than a flat $200 extra, because the "13th payment" effect is spread gradually across the year rather than added as a lump amount every single month.

Because $200 extra per month is slightly more principal reduction than biweekly's effective $189, it saves marginally more interest ($114,979 vs. $110,411) and pays off 3 months sooner in this example. The size of the extra payment matters more than which method delivers it.

Either way, the early years of savings come cheap: extra principal paid off early avoids interest for the entire remaining term, so the same $200 applied in year 1 saves far more interest than $200 applied in year 20.

Biweekly plans are appealing because they don't require deciding on a dollar amount; you're automatically making an extra payment a year. But a plain extra monthly payment of a similar size accomplishes the same thing, and is easier to adjust or pause if your budget changes.

Whichever method you use, extra payments only work if your lender actually applies them to principal rather than to future payments. Confirm that with your servicer before committing to a plan.

Whether prepaying even beats investing the same money is its own question, weighed in the guide on making extra loan payments. If a lower rate would help more than extra principal, compare the numbers on a refinance, or drill into the month-by-month amortization schedule to see exactly where each dollar goes.