Biweekly Mortgage Calculator

Biweekly payment = monthly ÷ 2, paid every two weeks → 26 a year = 13 monthly-equivalents. The 13th is an annual principal prepayment. The loan is amortised on the true biweekly period (rate ÷ 26), not approximated by an annual lump.

The 13th payment, hidden in plain sight

There are 52 weeks in a year, so paying every two weeks means 26 payments. If each is half your normal monthly amount, that adds up to 26 × ½ = 13 monthly payments a year — one more than the 12 you would make paying monthly. That extra payment is not a trick of accounting; it is real money, and because it lands on the principal, every future month’s interest is charged on a smaller balance. On a long mortgage the effect compounds into years off the term and a large slice of interest saved, all without a payment you would notice being larger.

This calculator models the true biweekly schedule — amortising on a two-week period at the annual rate divided by 26 — rather than faking it with one annual lump, so the years and interest saved are accurate. It shows the biweekly payment, how much sooner the loan clears, the interest avoided, and the new payoff date against the monthly baseline.

Worked example — a $300,000 loan at 6.5% over 30 years: The monthly payment is about $1,896; biweekly is half that, $948, every two weeks. That clears the loan in about 24.1 years instead of 30 — nearly 6 years early — and saves roughly $88,000 in interest.

Why it works — and the catch to watch

The power comes from two things at once: the extra annual payment, and the fact that interest on a mortgage is front-loaded, so cutting principal early saves the most. Biweekly does both automatically, which is why it is such a painless way to get ahead. You can push it further with a small extra on each payment or a one-time lump — enter them under the advanced options to see the combined effect. If you pay PMI, biweekly also reaches the 20%-equity threshold sooner, dropping the insurance earlier; add your home’s value to see by how much.

One caveat: a true biweekly plan means paying every two weeks, and some lenders charge a fee to set one up or only sweep the extra annually. You can usually get the same result for free by simply paying one extra month’s worth of principal each year yourself, or adding a twelfth of a payment to each monthly cheque. The saving is in the extra principal, not the fortnightly timing — so do not pay for the privilege.

Already partway through your loan?

Switching to biweekly works at any point, not just at the start — though the earlier you do it, the more you save, because there is more interest left to avoid. If you are partway through, enter your current balance as the loan amount and the remaining term as the term, and the calculator compares carrying on monthly against switching to biweekly from here. The years and interest saved are measured from today, so you see the benefit of switching now rather than the benefit you would have had from day one.

The chart makes the gain visual: two balance curves, monthly and biweekly, starting together and diverging as the biweekly line pulls below — the horizontal gap between them at any balance is the time you save, and the area between them is, roughly, the interest.