26 half-payments a year is 13 monthly payments, not 12
A biweekly mortgage calculator using true 26-payment amortization: half your payment every fortnight is thirteen monthly payments a year, not twelve.
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Interest saved with true biweekly
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Three approaches compared
Detail
⚠Many servicers will not credit a payment until a full monthly amount has arrived — they hold your half-payment and apply it with the next one. That turns true biweekly into the monthly approximation, which saves slightly less. Confirm how yours handles it before signing up for a paid biweekly service.
Balance over time, biweekly vs standard
Years
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How this is calculated
A true biweekly schedule charges half your monthly payment every fourteen days. Because a year holds 26 fortnights rather than 24, you make the equivalent of thirteen monthly payments instead of twelve. That thirteenth payment goes entirely against principal, and compounding does the rest.
There is a second, simpler version: keep paying monthly but add one twelfth of your payment each month. The totals are close but not identical — true biweekly retires principal slightly faster because the money arrives earlier in each cycle. This calculator shows both, because which one you actually get depends on your servicer.
Both approaches add roughly one extra monthly payment a year. True biweekly compounds on a 26-period year, the approximation on a 12-period year, which is why the results differ slightly.
Worked example
A $300,000 loan at 6.5% over 30 years.
Standard monthly payment$1,896.20
Total interest over 360 months$382,633
True biweekly payoffabout 25.7 years
Interest savedroughly $70,000
Do not pay someone to do this
Third-party biweekly conversion services charge a setup fee and often a per-transaction fee for something you can do yourself for free. The identical result comes from dividing your payment by twelve and adding that to each monthly payment, marked as principal only. If your servicer accepts extra principal payments — and almost all do — there is no reason to pay a middleman.
Check it is applied to principal
An extra payment only helps if it reduces principal. Some servicers default to holding overpayments in suspense, or applying them to the next scheduled payment instead, which achieves nothing. Label extra payments explicitly as principal-only and check the following statement to confirm the balance moved.
Whether it is the best use of the money
Paying down a mortgage returns exactly your interest rate, guaranteed and tax-free in effect. That is genuinely good at 6.5%. But if you have credit card debt at 20%, or an employer match you are not capturing, those come first. And if your rate is 3%, money is very likely better deployed elsewhere.
Frequently asked questions
Why does biweekly work at all?
Twenty-six half-payments across a year equal thirteen full monthly payments, not twelve. That thirteenth payment goes entirely against principal, and every dollar of principal retired early stops accruing interest for the whole remaining term. On a thirty-year loan the compounding effect of that one extra payment a year is worth several years off the term.
Is true biweekly better than adding a twelfth each month?
Only marginally. True biweekly gets the money to the lender slightly earlier in each cycle, so a little less interest accrues, but the difference over a thirty-year loan is usually small. The thirteenth payment is doing almost all the work in both approaches, which is why the do-it-yourself version is generally the sensible choice.
Will my lender actually apply payments biweekly?
Many will not. A large number of servicers hold partial payments in suspense until a full monthly amount has arrived, then apply it as a single monthly payment. That converts true biweekly into the monthly approximation, which saves slightly less. Ask your servicer directly how they handle partial payments before signing up for anything.
Should I pay a service to set this up?
No. Third-party biweekly conversion services charge a setup fee and often a per-transaction fee for something you can do yourself at no cost. Divide your monthly payment by twelve, add that amount to each monthly payment, and mark it principal-only. The result is effectively identical and you keep the fees.
Does this affect my escrow?
No. Property taxes and homeowners insurance are collected separately through your escrow account and are unaffected by how you pay principal and interest. Only the principal and interest portion of the loan is accelerated, so your escrow analysis and any shortage or surplus continue to work exactly as they did before.
Can I stop if money gets tight?
If you are doing it yourself, yes, entirely. Skip the extra payment in any month you need to, with no consequence and no penalty, because the scheduled payment is still being met. If you have signed up to a formal biweekly program through a third party it may be contractual, which is another good argument for the do-it-yourself route.
Estimates for general information only, not mortgage advice. Principal and interest only — property tax, insurance and PMI are excluded. Confirm with your servicer how partial and extra payments are actually applied.