Biweekly Mortgage Payment Calculator
How It Works
A biweekly mortgage payment schedule means paying half of your normal monthly payment every two weeks, instead of paying the full amount once a month. Because a year has 52 weeks, this works out to 26 half-payments — the equivalent of 13 full monthly payments per year instead of 12. That one extra payment per year goes entirely toward principal, and it accelerates your payoff far more than most homeowners expect.
This calculator runs a true biweekly simulation, not the simplified "add 1/12th of a payment" approximation some lenders and calculators use. Every two weeks, we apply half your standard monthly payment against your remaining balance using a true biweekly interest rate — the same way a real biweekly payment plan would post to your loan. Because principal gets reduced more frequently throughout the year, this approach saves slightly more interest than the once-a-year "extra payment" shortcut, and it's the more mathematically accurate model of what actually happens to your balance.
The results below show your standard monthly schedule side by side with the true-biweekly schedule, so you can see exactly how much faster your loan pays off and how much interest you keep in your pocket instead of handing to the lender.
One important disclosure: some lenders and third-party companies offer a formal "biweekly payment program" that automates the biweekly withdrawal — and many of these programs charge a setup fee or an ongoing service fee, sometimes $300–$400 or more. This calculator models the payment schedule and its mathematical effect on your loan only; it does not include any lender or third-party program fee. You can achieve the identical result for free by simply making one extra full monthly payment per year, or by paying 1/12th extra with every monthly payment, directly through your existing loan servicer — as long as your servicer applies extra payments to principal and doesn't charge a prepayment penalty.
Biweekly acceleration works best on higher-rate, longer-term loans, where more of each payment currently goes to interest. On a shorter-term or already low-rate loan, the dollar savings will be smaller, though the percentage benefit is still real. Always confirm with your loan servicer that extra principal payments are applied immediately and not held in a suspense account until a full payment accumulates.
Formula Breakdown
STANDARD MONTHLY PAYMENT (unchanged, composed from the mortgage calculator):
M = P[r(1+r)^n] / [(1+r)^n − 1]
Where P = principal, r = monthly rate (annual rate / 12), n = total months
TRUE BIWEEKLY SIMULATION (26 payments per year, not an approximation):
Half-Payment = Monthly Payment / 2
Biweekly Rate = Annual Rate / 100 / 26
Each of the 26 periods per year:
Interest = Remaining Balance × Biweekly Rate
Principal Paid = Half-Payment − Interest
Remaining Balance = Remaining Balance − Principal Paid
...repeated until the balance reaches $0 (capped at a 40-year safety limit)
RESULTS:
Biweekly Term (months) = (Total Periods to Payoff / 26) × 12
Months Shaved = Standard Term (months) − Biweekly Term (months)
Interest Saved = Standard Total Interest − Biweekly Total Interest
EXAMPLE ($400,000 at 6.5% for 30 years):
Standard monthly payment: $2,528.27/month, $509,177.20 total interest over 360 months
Biweekly: $1,264.14 every 2 weeks, meaningfully fewer months to payoff and
measurably less total interest — both computed directly from the simulation,
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