Biweekly Payment Calculator
Half your mortgage payment every two weeks adds up to 13 full payments a year instead of 12. See exactly what that extra payment does to your payoff date and lifetime interest.
Monthly vs. biweekly
Example: $200,000 at 6% over 30 years → debt-free 5 yr 6 mo sooner, saving $49,624.
Companion guide: Reading an amortization schedule walks through the month-by-month schedule this comparison is measured against — how each row splits interest from principal, and what a fixed extra payment does to the rows. This page covers what the biweekly engine does differently: the two-week period, the half-payment, and the 13th payment. Every explainer on the site is listed under Guides.
The worked example: one extra payment a year
On the worked $200,000 loan at 6% over 30 years — the same fictional reference loan the methodology page validates the engine against — the monthly schedule costs $1,199.10 a month and $231,676 of lifetime interest. Switch to $599.55 every two weeks and the loan retires in 24 yr 6 mo — 5 yr 6 mo early — with $49,624 of interest saved, 21.4% of the interest the monthly schedule would have charged. Nothing exotic happened: the calendar contributed a 13th payment each year, and every extra dollar reduced the balance interest is charged on. Every figure on this page is computed when the page is built by the same tested engine that powers the calculator above; if the copy and the code ever disagreed, the site would fail to build rather than publish inconsistent numbers.
What the engine computes, step by step
The form hands your three inputs to one engine function, which validates them, runs the steps below in order, and returns a typed result — or an explicit, human-readable error if an input cannot be used. The interface only formats what comes back; it never does arithmetic of its own.
- The monthly payment is the standard amortized-loan (PMT) formula with monthly compounding, the convention behind US mortgages and most consumer loans: the annual rate ÷ 12 is the monthly rate, years × 12 is the number of payments (360 in Example A), and the result is the one fixed payment that retires the balance exactly at the last month — $1,199.10 here.
- The monthly schedule's interest is stated in closed form: payment × number of payments − loan amount, or $1,199.10 × 360 − $200,000 = $231,676. The month-by-month sum lands on the same figure; the comparison below shows both.
- The biweekly payment is half the monthly payment: $599.55. It is not adjusted so that 26 of them equal 12 monthly payments — that difference is the whole point.
- The biweekly periodic rate is the annual rate ÷ 26, the two-week counterpart of the monthly schedule's annual rate ÷ 12. On Example A's opening balance one period's interest is $461.54.
- The schedule runs one period at a time. Each period the engine charges interest on the balance still outstanding, credits the rest of the half-payment to principal, and repeats until the balance is gone. In the final period it credits only what remains, so the last half-payment is smaller than the rest. A half-payment that failed to cover a period's interest would stop the engine with an error; a PMT-derived half-payment always exceeds it.
- Payoff time is the period count converted to months: periods ÷ 26 × 12. Example A clears in 638 half-payments, which is 294.46 months, or about 24.5 years.
- Months saved = the scheduled months − the biweekly payoff months, and interest saved = the monthly schedule's interest − the biweekly schedule's interest: $231,676 − $182,052 = $49,624.
| Line | How the engine computes it | Value |
|---|---|---|
| Monthly payment | PMT on $200,000 at 6% over 360 months | $1,199.10 |
| Biweekly payment | Monthly payment ÷ 2 | $599.55 |
| Monthly schedule interest | $1,199.10 × 360 − $200,000 | $231,676 |
| Biweekly schedule interest | Summed over 638 two-week periods at 6% ÷ 26 | $182,052 |
| Biweekly payoff time | 638 ÷ 26 × 12 months, rounded on screen | 24 yr 6 mo |
| Months saved | 360 − 294.46, rounded on screen | 5 yr 6 mo |
| Interest saved | $231,676 − $182,052 | $49,624 |
Period one, against month one
The two schedules start from the same balance and diverge from the first payment. On the monthly schedule, month one charges $200,000 × 6% ÷ 12 = $1,000.00 of interest, so $199.10 of the $1,199.10 payment reaches principal. On the biweekly schedule, period one charges $200,000 × 6% ÷ 26 = $461.54, so $138.01 of the $599.55 half-payment reaches principal — and the second period is charged on a balance that is already smaller. Two half-payments do not make a month, though; the schedules are compared on a whole-loan basis, by the total interest each one charges and the time each one takes to reach zero.
Biweekly crediting against a monthly extra
The biweekly engine and the month-by-month schedule engine behind the Mortgage Payoff Calculator and the Amortization Calculator are different functions, so the page runs both on Example A. The baselines agree: the biweekly engine's closed-form monthly interest is $231,676, and the schedule engine, summing the same 360 payments one month at a time, records $231,676 — the build verifies the match. The nearest monthly imitation of a biweekly schedule adds one-twelfth of the payment, $99.93, to each month, so twelve months carry the same extra payment that 26 half-payments do. Run by the schedule engine, that pays the loan off in 24 yr 7 mo, 5 yr 5 mo early, saving $49,110; the biweekly engine reports 5 yr 6 mo and $49,624. The $514 between them is the net effect of accruing interest and crediting principal every two weeks instead of every month; the shared 13th payment accounts for the rest.
A second loan, and a shorter term
Example B is a fictional $340,000 loan at 6.75% over 30 years: a $2,205.23 payment, a $1,102.62 half-payment, and $108,293 of interest saved, with the loan clearing 6 yr 1 mo early. Example C keeps the same loan and rate over 15 years instead; the payment rises to $3,008.69, and the biweekly schedule finishes 1 yr 11 mo early, saving $28,821 of a much smaller $201,565 total.
| Line | Example B — 30 years | Example C — 15 years |
|---|---|---|
| Monthly payment | $2,205.23 | $3,008.69 |
| Biweekly payment | $1,102.62 | $1,504.35 |
| Monthly schedule interest | $453,884 | $201,565 |
| Biweekly schedule interest | $345,591 | $172,744 |
| Biweekly payoff time | 23 yr 11 mo | 13 yr 1 mo |
| Months saved | 6 yr 1 mo | 1 yr 11 mo |
| Interest saved | $108,293 | $28,821 |
The extra payment each year is always one monthly payment, so a shorter term makes it larger in dollars — but leaves fewer years to apply it and a smaller interest total to work against, so both the months saved and the interest saved are smaller. The engine compares; whether a higher payment for fewer years fits a household's budget is not a question the arithmetic answers.
How to read the result
- The headline line — "Debt-free … sooner, saving …" — is the months saved, rounded to the nearest whole month, and the interest saved, rounded to whole dollars: 5 yr 6 mo and $49,624 in Example A.
- Biweekly payment (half the monthly) is the monthly PMT amount ÷ 2, shown to the cent — $599.55. The monthly payment is twice this figure.
- Monthly schedule interest is the closed-form total for the unchanged schedule, $231,676 here. Add the loan amount for the total of payments on that schedule: $431,676.
- Biweekly schedule interest is the sum of every two-week period's interest, $182,052 here, making $382,052 of total payments.
- Biweekly payoff time is the period count converted to months and rounded on screen: 24 yr 6 mo for Example A.
Money is shown to the cent, or to whole dollars for large totals like lifetime interest; internally every calculation keeps the full precision of IEEE-754 double-precision arithmetic, and nothing is rounded between steps. Your lender's figure may differ by a few cents depending on their rounding and day-count conventions — the difference is presentational, not an error. Because the payoff time is rounded to whole months, 5 yr 6 mo saved may stand for a value a few weeks either side of it. The Copy result button places a one-line summary — the biweekly payment, the payoff time, and the interest saved — on your clipboard.
Where the calculator stops
The limits are the engine's, and the methodology page states them. The calculators model fixed-rate, fully amortizing loans. They do not model adjustable-rate mortgages, interest-only periods, balloon payments, or negative amortization: whatever rate you enter is held fixed for every period of the comparison. The engine models one arrangement — half the monthly payment credited every two weeks, interest accrued per two-week period from the first period — and does not know how your servicer collects, holds, or posts payments, whether extra amounts are applied to principal, or whether any fee or prepayment term attaches to the loan; none of those are inputs. It has no calendar: months saved are a count of scheduled months removed, not a date. There are no tax, insurance, PMI, HOA, closing-cost, or points inputs; the Mortgage Calculator carries the housing lines. Inputs are validated before any arithmetic runs: a term beyond the engine's limit is refused with its own message — "Terms are limited to 60 years." — a rate beyond its limit with "Enter an interest rate below 100%.", and non-numeric, negative, or infinite values return a plain-language error instead of a number. And a correct calculation can still be the wrong calculation for your situation — choosing the right loan for a real-world decision is judgment we cannot automate.
Frequently asked questions
Why does paying biweekly pay the loan off early?
A year holds 26 two-week periods, so half-payments every two weeks add up to 13 full payments instead of 12 — a whole extra payment a year, applied straight to principal. On the worked $200,000 loan the 26 half-payments come to $15,588.31 a year against $14,389.21 on the monthly schedule: a difference of exactly one monthly payment, $1,199.10. The magic is not the frequency; it is the extra payment the calendar smuggles in.
How does the engine turn the monthly payment into a biweekly one?
It computes the standard monthly payment first — the PMT formula with monthly compounding — and halves it: $1,199.10 becomes $599.55 on the worked loan. It is always exactly half of the fixed monthly amount, which is what makes the 13th payment appear.
Is this the same as my servicer’s "biweekly program"?
Not necessarily. The engine models one arrangement — half the monthly payment credited every two weeks, interest accrued per two-week period — and does not know how any particular servicer collects, holds, or posts payments. If half-payments are collected every two weeks but posted monthly, the schedule being run is not this one, and the figures here overstate the saving. Confirm how your servicer applies extra amounts.
Does the timing of interest matter?
Slightly, and the page measures it. This calculator models true biweekly crediting: interest accrues per two-week period at the annual rate ÷ 26. The Mortgage Payoff Calculator's engine runs the nearest monthly equivalent — one-twelfth of a payment added to each month — and on the worked loan it saves 5 yr 5 mo and $49,110, against 5 yr 6 mo and $49,624 here. The dominant effect, the 13th payment, is identical either way; the two-week period accounts for the remainder.
How is the "Monthly schedule interest" line computed?
In closed form: the fixed monthly payment × the number of payments − the loan amount, which on the worked loan is $1,199.10 × 360 − $200,000 = $231,676. The Amortization Calculator sums the same schedule one month at a time and arrives at $231,676; the two agree to the dollar, and the build checks that they do.
What happens at a 0% rate?
Every interest line is zero and the acceleration is pure calendar. A fictional $120,000 loan at 0% over 10 years has a $1,000.00 monthly payment and a $500.00 half-payment; 240 half-payments clear the balance, which the engine reports as 9 yr 3 mo — 9 mo sooner than the 120-month schedule — with $0 of interest saved.
Why is the payoff time shown in whole months when payments are two-weekly?
The engine counts two-week periods — 638 on the worked loan — and converts them to months as periods ÷ 26 × 12, which gives 294.46 months. The interface rounds that to the nearest whole month, 24 yr 6 mo, and does the same for the months saved. The final, smaller half-payment is counted as a full period.
Does the calculator say whether to pay biweekly?
No. It compares two schedules for the same loan and reports the difference in payoff time and interest. Whether the higher annual outlay — one extra monthly payment a year — fits a household’s budget, or competes with other uses of the money, is not a question the arithmetic answers. The engine compares; the reader decides.
Not financial advice: a general educational estimate assuming true biweekly interest crediting — servicers that post monthly yield slightly smaller savings. Confirm how your servicer applies extra amounts. Values are processed locally in your browser and never transmitted. See the methodology page.