How this calculator works
An accelerated biweekly mortgage schedule replaces 12 monthly payments a year with 26 half-payments, paid every two weeks. Because a year has 52 weeks, 26 half-payments works out to 13 full monthly-equivalent payments instead of 12 — one extra payment's worth of principal every year, without the payment amount itself ever going up.
This calculator simulates the biweekly schedule period by period, applying half the standard monthly payment against the balance every two weeks at the equivalent two-week interest rate, rather than assuming a fixed number of years saved. That simulation is what produces the payoff time and interest savings below, so the result reflects the actual loan amount and rate entered rather than a generic rule of thumb.
The formula
Standard monthly payment: M = P × i ÷ (1 − (1 + i)^−n)Biweekly payment = M ÷ 2, paid every two weeks (26 times a year)Each two-week period: balance = balance − (biweekly payment − balance × annual rate ÷ 26)P is the loan amount, i the monthly rate (annual rate ÷ 12), and n the number of monthly payments (years × 12) for the standard schedule. The biweekly simulation uses the nominal annual rate divided by 26 periods for each two-week step, the standard convention for converting an annual rate to a shorter period.
Worked example: $200,000 at 6% for 30 years
- Standard monthly payment on $200,000 at 6% over 360 months = $1,199.10, for total interest of about $231,676 over 30 years.
- Biweekly payment = 1,199.10 ÷ 2 = $599.55, paid every two weeks (26 times a year).
- Simulating that payment every two weeks, the balance reaches zero after 638 periods — about 24.5 years, roughly 5.5 years sooner than the 30-year standard schedule.
- Total interest under the biweekly schedule is about $182,052, a savings of roughly $49,624 compared with the standard monthly schedule.
Frequently asked questions
Why does paying half the payment twice a month not do the same thing?
Paying half the monthly payment on two fixed dates each month (24 times a year) is mathematically identical to the standard monthly schedule — it is still 12 full payments a year. The acceleration only happens with a true biweekly schedule, paid every two weeks, which lands on 26 half-payments (13 full payments) because of the extra two paydates a true 52-week year contains.
Do I need my lender's permission to pay biweekly?
Often yes. Many lenders apply payments as received rather than holding a partial payment until it completes a full monthly payment, in which case an informal biweekly schedule may not accelerate the loan at all, or may even trigger fees. Ask your servicer whether they offer a formal biweekly program before assuming the payments will apply as this calculator models.
Is this the same as making one extra monthly payment a year?
It has a very similar effect — 26 half-payments a year works out to 13 monthly-equivalent payments, the same 1-extra-payment-per-year result some borrowers achieve by simply adding 1/12 of a payment to every monthly bill. The exact payoff time can differ slightly because of how the extra amount is timed and compounded, but both approaches meaningfully shorten a long fixed-rate loan.
Does a higher interest rate change how much biweekly payments help?
Yes — the dollar amount of interest saved is generally larger at higher rates, since more interest is accruing on the balance that gets paid down faster. Try a few different rates in this calculator to see the effect on your own loan amount and term.
Can I get the same result by just paying extra each month instead?
Often, yes — sending an equivalent extra amount with your regular monthly payment achieves a similar effect without needing a special biweekly program. See the extra payment calculator to compare a fixed extra monthly amount directly against your standard schedule.