Biweekly mortgage payments: how much do you really save?

By DecisionSheet · Updated October 10, 2026 · 2026 tax figures

A biweekly mortgage plan pays half the monthly payment every two weeks. There are 26 two-week periods in a year, so that is 26 half-payments, or 13 full payments, where the normal schedule makes 12. The thirteenth payment goes to principal, and that is the entire mechanism: a biweekly plan is an extra payment a year, 8.3% on top of each month's payment, with a calendar wrapped around it.

DecisionSheet's mortgage payoff vs. invest calculator has no biweekly switch, and does not need one. It takes an extra monthly amount, or an extra annual one, and runs the loan to the end both ways. This page uses it to put a figure on the thirteenth payment, to show what moves that figure, and to compare it with what the paid biweekly programs charge.

The example

• The loan. The calculator's default house: $500,000 with $100,000 down, so $400,000 borrowed over 30 years at 6.5%. For context, the Freddie Mac survey's average 30-year fixed rate was 7.40% as of October 8, 2026 (Freddie Mac PMMS).
• The payment. Principal and interest of $2,528.27 a month, so a biweekly plan would draw $1,264.14 every two weeks. Paid on schedule, the loan costs $510,178 in interest.
• The extra. Twelve payments come to $30,339 a year; 13 come to $32,868. The difference is one payment, $2,528.27, which is $210.69 a month.

One extra payment a year, two ways

The calculator can apply the extra payment as $210.69 every month, which is how a biweekly plan's extra accumulates, or as one full payment of $2,528.27 at the end of each year, which is what "make a thirteenth payment" usually means in practice.

Open each: $210.69 a month · one payment at year end. Each differs from the plain loan in that one input.

Either way the loan ends close to six years early and about a fifth of the interest never gets charged: 23% of it with the monthly twelfth. Spreading the extra through the year beats saving it up for December by $4,363 of interest and 2 months, because each twelfth starts reducing the balance the month it is paid. A true biweekly plan, with half-payments posted every 14 days and interest accrued on each, does slightly better again than the monthly row for the same reason; the calculator steps by the month and does not model it, so its figures are a little conservative.

The required payment is unchanged throughout. The extra shortens the loan; it never lowers the monthly bill, and the 8.3% is a commitment for as long as the loan lasts.

Why 8.3% more buys so much

Each month the loan charges one-twelfth of 6.5% on whatever balance is outstanding, and the fixed payment covers that interest before it touches principal. An extra $210.69 goes entirely to principal, and every dollar of principal repaid is missing from every interest charge that follows. That is why a payment 8.3% larger removes 23% of the interest. What an extra $100, $250 or $500 a month does to a 30-year mortgage works through the same arithmetic at round amounts.

What changes the answer

The rate. The thirteenth payment is worth more on a dear loan. The twelfth itself rises with the rate, because the payment does, and each dollar of it avoids more interest.

Open each: 4.0% · 7.5%.

When you start. A plan begun years into the loan has less interest left to avoid. The calculator can show this: enter the balance at that point over the years left at the same rate, and the payment comes out the same $2,528.27, within a cent of rounding.

Open each: 10 years in · 20 years in. Started 20 years in, the plan still ends the loan 1 year early, for $9,100.

Selling or refinancing. The interest saved accrues over the whole shortened loan. A borrower who sells in year seven keeps only the interest avoided up to then, plus a lower balance at payoff.

Paid programs and their fees

Lenders and third parties sell biweekly plans, and the plan itself adds nothing a borrower cannot do alone: pay $210.69 extra each month marked for principal, or $2,528.27 once a year, and the loan follows the table above. The fees are what the program costs on top. Two CFPB actions put numbers on them. In 2015 the Bureau sued Nationwide Biweekly Administration, alleging a setup fee of up to $995 and $84 to $101 a year in processing fees for a program that collected half the monthly payment every two weeks (CFPB, May 2015). The same year it ordered Paymap and LoanCare to refund fees on an "Equity Accelerator" program, a $295 enrollment fee plus typically $2.50 per debit, that drew money every two weeks but, the Bureau found, paid the mortgage on its original monthly schedule (CFPB, July 2015).

Over the 24 years the example loan runs with the extra, fees at those rates come to $3,025 to $3,436 for the first program and $1,866 for the second, against $116,342 of interest saved. The fees do not undo the saving; they are a charge for a result the extra payment produces on its own. Those figures are what the Bureau alleged a decade ago, not a survey of today's programs, and a lender's own plan may be free. Whatever the program, ask the servicer when the half-payments are applied: held until the full payment is in hand, they save nothing the monthly extra would not.

Prepay the twelfth, or invest it?

Every dollar of extra principal earns the loan's rate, compounded monthly: 6.70% on this loan, which the calculator reports as the break-even market return, and which is the same whichever way the extra is paid. At its default 8% assumed return the verdict favors investing the $210.69 instead, by $54,820 at the end of 30 years. That verdict rests entirely on the return assumed; Pay off a 3% mortgage or a 7% mortgage early? explains the comparison and how it moves with the rate.

Assumptions and limits

• Fixed-rate, fully amortizing loan: the standard monthly payment, with interest charged monthly at one-twelfth of the annual rate. The model steps by the month, so the "biweekly" rows are its two monthly equivalents; the small extra benefit of posting half-payments every 14 days is not modeled.
• The extra starts in month one of each scenario and continues until the loan is paid off. The late starts are the same loan picked up at its balance after 10 or 20 years.
• No program fees, and no prepayment penalty. The CFPB says a penalty typically applies to paying off the whole balance within a set number of years, not to small extra payments; the Loan Estimate lists whether a loan has one (CFPB).
• Every extra dollar is credited to principal in the month it is paid. A servicer that holds a half-payment, or applies an overpayment to next month's bill, changes the result.
• Escrow: the calculator adds property tax and insurance to the monthly total it shows, but they have no effect on the payoff date or the interest saved.
• Pre-tax, in nominal dollars: no mortgage interest deduction, no tax on the investment comparison, no adjustment for inflation.

Method and sources

The model is calculateMortgage in the mortgage payoff vs. invest calculator. The required payment is the standard fixed-rate amortization formula; the loan is run month by month on schedule and again with the extra applied to principal, and interest saved and time cut are the differences between the two runs. The break-even return is solved against the same simulation. Every figure above comes from running the model on the inputs in the scenario links; the fee totals are the cited fees multiplied over the shortened loan's length.

• Freddie Mac, Primary Mortgage Market Survey: 30-year fixed-rate average of 7.40% as of October 8, 2026.
• CFPB: CFPB files suit against Nationwide Biweekly, May 11, 2015: the alleged $995 setup fee and $84 to $101 annual processing fees.
• CFPB: action against Paymap and LoanCare, July 28, 2015: the $295 enrollment fee, the $2.50 per-debit fee, and the finding that the program did not make more frequent payments on the mortgage.
• CFPB: What is a prepayment penalty?

Open this scenario in the calculator

All figures on this page come from the Mortgage Payoff vs. Invest calculator. Change any input there and the numbers update.