Worked derivation
Biweekly mortgage payments: what the thirteenth payment actually does
The benefit is real, and it has almost nothing to do with paying fortnightly.
The whole mechanism
26 half-payments a year is 13 monthly payments, not 12.
On $320,000.00 at 6.706% over 30 years the contractual payment is $2,066.16.
Twelve of those in a year is $24,793.92. Twenty-six halves is $26,860.08 — a difference of $2,066.16, which is exactly one payment.
That single extra payment a year removes 72 months and $99,532.52 of interest from the schedule.
Where the saving comes from
A year has twelve months and twenty-six fortnights. Pay monthly and you make twelve payments; pay half the monthly amount every fortnight and you make twenty-six halves, which is thirteen wholes. The extra thirteenth payment has no interest of its own to cover, so all of it reduces the balance — and a smaller balance is charged less interest in every month that follows.
That compounding is the entire effect. It is not that fortnightly payments are charged differently, and it is not a trick of the calendar. It is one more payment a year, doing what any extra payment does.
26 × (monthly payment ÷ 2) = 13 × monthly payment
13 − 12 = 1 extra payment a year
Two loans, computed
Both rows are produced by running the mortgage engine at build time, not looked up. The second is the loan the CFPB used in its own enforcement action against a biweekly payment company, so the arithmetic here can be read against their figures.
| Loan | Payment | Paid fortnightly | Extra a year | Term becomes | Interest saved |
|---|---|---|---|---|---|
| $320,000.00 at 6.706% | $2,066.16 | $1,033.08 | $2,066.16 | 24y 0m from 30y 0m | $99,532.52 |
| $160,000.00 at 4.125% | $775.44 | $387.72 | $775.44 | 25y 10m from 30y 0m | $18,840.18 |
Interest is charged monthly on the opening balance, rounded to the cent every month, with the final payment reduced to clear the balance exactly.
The same money, paid monthly
If the effect is one extra payment a year, then dividing that payment across the twelve months puts the same money against the balance on almost the same schedule. On $320,000.00 at 6.706% that is $172.18 added to each monthly payment — $2,066.16 a year, which is what the fortnightly schedule delivers.
This page models exactly that: the extra spread evenly, month by month. It is the closest a monthly engine gets to money that accumulates fortnightly, and it is why the figures above are described as the effect of the thirteenth payment rather than of fortnightly billing.
What this page does not model
A true fortnightly accrual. On a genuinely fortnightly schedule, half a payment lands mid-month and reduces the balance a fortnight before a monthly model can register it. That is a real effect and it is small beside the thirteenth payment. This page does not claim it.
How your servicer applies the money. The figures here assume every extra cent reduces principal in the month it arrives. Some servicers hold partial payments in suspense until a full payment accumulates, which changes the timing. The CFPB describes programmes that collect fortnightly and forward monthly — in that arrangement the fortnightly part does nothing at all, and the annual extra is the whole of it.
Anything about your loan in particular. Early repayment charges, escrow, insurance, rate changes on an adjustable loan and fees are all outside this arithmetic, and every one of them can move the real answer.
What the fee changes
Some companies sell enrolment in a biweekly programme. The arithmetic above does not change when a fee is charged — but the money left over does, and that is a documented matter of record rather than an opinion.
The CFPB sued Nationwide Biweekly Administration over its programme, alleging a setup fee of up to $995 plus annual processing fees of $84 to $101, and that consumers will pay more in fees than they save in interest for the first several years
. The Bureau's own example was a $160,000.00 mortgage at 4.125%, on which it said a consumer would need nine years to recoup the fees.
That is the same loan as the second row of the table above, where the extra payment removes $18,840.18 of interest across 25y 10m. Both figures are real; they are simply measured over different periods, which is what the Bureau's nine-year point is about.
Whether any particular programme charges a fee, and whether your servicer accepts extra principal directly, are questions for your servicer and your note. This page computes the arithmetic; it does not know your loan and does not tell you what to do with it.
Common questions
- Why does paying every two weeks pay a mortgage off faster?
- Not because of the fortnightly timing — because of the count. Twenty-six half-payments is thirteen monthly payments, so a year of biweekly payments contains one more payment than a year of monthly ones. On $320,000.00 at 6.706% that extra is $2,066.16 a year, and it removes 72 months and $99,532.52 of interest.
- Is it the same as paying a bit extra every month?
- Very nearly, and that is the point. Adding $172.18 to each monthly payment on $320,000.00 at 6.706% puts the same $2,066.16 a year against the balance. The remaining difference is timing within the month, which is small next to the extra payment itself.
- Does this page model a true fortnightly schedule?
- No, and that is stated rather than glossed. It models one extra payment a year, spread evenly month by month, using the same monthly engine as the mortgage calculator. A true fortnightly schedule credits half a payment mid-month, which reduces the balance slightly earlier than a monthly model can express. That effect is real and small; the thirteenth payment is where essentially all of the difference comes from.
- Do biweekly payment plans cost anything?
- Some do. The CFPB sued Nationwide Biweekly Administration over its programme, alleging a setup fee of up to $995 plus annual processing fees of $84 to $101, and that consumers "will pay more in fees than they save in interest for the first several years". Whether any particular plan charges a fee, and how your servicer applies extra money, are questions for your servicer and your note — not for a calculator.
- Will my servicer apply an extra payment to principal?
- That depends on your servicer and how the payment is labelled. Extra money is only worth what this page computes if it reduces the principal rather than sitting in suspense or being treated as a payment made early. Ask how they apply it before assuming, and check the next statement.
- Does the arithmetic depend on the country?
- The counting does not — twenty-six halves is thirteen wholes anywhere. The rest depends on your loan: how interest accrues, whether early repayment carries a charge, and how your lender applies extra money. The sources below are US, and the schedule here uses the US monthly convention.
Sources
- CFPB — Someone offered me 26 bi-weekly mortgage payments a year for a fee — retrieved 2026-08-12
- CFPB — Suit against Nationwide Biweekly over mortgage savings claims — retrieved 2026-08-12
- CFPB — What is an amortization schedule? — retrieved 2026-08-12
- Every figure in the table and the prose is produced at build time by the same engine the mortgage calculator runs, from the loan amounts and rates shown beside it. The fee figures and the nine-year recovery period are the CFPB's, quoted from the filing above and not recomputed here.
Written and maintained by Vikash Singh. Last verified 2026-08-12.