Bi-weekly mortgage calculator

Bi-weekly mortgage calculator

Switching from monthly to bi-weekly mortgage payments is one of the simplest mortgage acceleration strategies — and one of the most effective. The math is counterintuitive but real: 26 half-payments per year equals 13 full monthly payments, not 12.

The 26-payment trick

There are 52 weeks in a year. Paying every two weeks = 26 payments per year. At half a monthly payment each time, that's 13 full monthly equivalents — one free extra principal payment every year. On a $300,000 30-year loan at 7%, that extra payment saves roughly 5 years and $60,000+ in interest.

How to calculate bi-weekly savings

Bi-weekly payment = monthly payment / 2

Extra annual principal = 1 monthly payment equivalent

The interest savings come from simulating two amortization schedules: one with 12 monthly payments and one with 26 bi-weekly payments applied as they come in, each time reducing the balance before the next interest accrual.

Why timing matters

In standard monthly amortization, interest accrues on the outstanding balance for the full month. In bi-weekly amortization, each mid-month payment reduces the balance two weeks earlier, cutting the interest for the second half of the month. This small timing advantage compounds over 30 years.

The DIY equivalent

You don't need to enroll in a bi-weekly program. Simply add 1/12 of your monthly payment to each monthly payment as extra principal. This produces mathematically identical results. On a $1,500 monthly payment, add $125 per month extra. Total extra per year = $1,500 = one full extra payment.

What this doesn't cover

This calculator uses a simulation approach to compute exact interest savings, not an approximation. It doesn't model variable-rate loans, interest-only periods, or escrow changes.