Paying half your mortgage payment every two weeks results in 26 half-payments a year, which equals 13 full monthly payments instead of 12 - one extra payment a year that goes straight to principal. On a typical 30-year loan, that single extra payment per year shortens the term by roughly 5 to 6 years and cuts tens of thousands of dollars in interest. This guide shows the exact math so you can judge the result yourself.
The engine: why 26 halves beat 12 wholes
A calendar year has 52 weeks. If you split your monthly mortgage payment in half and send that half every two weeks, you make 52 / 2 = 26 half-payments per year. Twenty-six halves add up to 13 whole payments. A standard monthly schedule only collects 12 whole payments a year. That difference - the 13th payment - is the entire trick.
Here is the key insight: the extra payment is not magic interest savings on its own. It works because the full amount of that 13th payment lands on principal, the part of the balance that you actually owe. Less principal means less interest charged next month, which means more of every future payment also attacks principal. The effect compounds, and the loan collapses years early.
Run your own loan through the Biweekly Mortgage Calculator to see your personal payoff date, then come back here to understand why the number looks the way it does.
A worked example: $300,000 at 6.5%
Take a 30-year fixed loan of $300,000 at a 6.5% annual rate. The required monthly payment is $1,896.20. Over the full 360 months you would pay $682,633.47, of which $382,633.47 is interest.
Now switch to the biweekly rhythm. You send $948.10 (half of $1,896.20) every two weeks. Across a year that is 26 x $948.10 = $24,650.65. Compare that to 12 monthly payments of $1,896.20 = $22,754.45. You paid $1,896.20 more in the year - exactly one extra monthly payment - without ever writing a big check.
| Approach | Payoff time | Total interest | Interest saved |
|---|---|---|---|
| Standard monthly (12/yr) | 30 years | $382,633.47 | - |
| Biweekly (26 halves/yr) | ~24.2 years | ~$294,511.68 | ~$88,121.79 |
That is roughly 5.8 years off the term and about $88,000 in interest saved on a single $300,000 loan - just from one extra payment a year applied to principal.
The savings scale with your loan and rate
Bigger balances and higher rates produce bigger savings, because there is more interest to avoid. The table below shows the biweekly effect across three 30-year loans, all recomputed.
| Loan / rate | Monthly payment | Standard interest | Time saved | Interest saved |
|---|---|---|---|---|
| $250,000 @ 6.0% | $1,498.88 | $289,595.47 | ~5.4 yrs | ~$61,388 |
| $300,000 @ 6.5% | $1,896.20 | $382,633.47 | ~5.8 yrs | ~$88,000 |
| $400,000 @ 7.0% | $2,661.21 | $558,035.59 | ~6.3 yrs | ~$136,566 |
Notice the pattern: the time saved clusters around 5 to 6 years no matter the balance, while the dollar savings climb sharply with the loan size and rate. That is why a one-line change to your payment schedule is one of the highest-return moves available to a homeowner.
The DIY shortcut: add 1/12 of a payment every month
You can get nearly the identical result without changing your payment frequency at all - just add one-twelfth of your monthly payment to each monthly check. One-twelfth of $1,896.20 is $158.02. Pay $2,054.22 each month and over a year you contribute exactly one extra payment, same as the biweekly plan.
How close is it? Using the $300,000 / 6.5% loan, the true biweekly schedule leaves $294,511.68 in interest, while the add-1/12 monthly method leaves $295,377.18. The difference over 24 years is about $865 - a rounding error on a near-$300,000 interest bill.
The 1/12 method has two advantages: it works even if your lender will not accept biweekly drafts, and the extra clearly lands on principal because you control the payment. If you would rather pick a round extra number instead of one-twelfth, model any figure with the Extra Payment Mortgage Calculator.
How biweekly differs from other accelerated methods
- Biweekly is a fixed system: half your payment, every two weeks, producing exactly one disciplined extra payment a year.
- Arbitrary extra payments let you throw any amount at principal whenever you have spare cash - more flexible, less automatic.
- A 15-year refinance forces a much larger required payment and locks you in, whereas biweekly keeps your low required payment if money gets tight.
To see the underlying loan mechanics first, the Mortgage Calculator shows the standard schedule, and our guide on how loan interest works explains why front-loaded interest makes early principal payments so powerful.
How to set up biweekly payments correctly
The math only works if the extra money actually reaches principal. Confirm the details before you start, and remember that the Consumer Financial Protection Bureau confirms lenders generally cannot refuse extra principal payments.
Try it yourself
Run your own numbers in the free Biweekly Mortgage Calculator — instant, private, no sign-up.
Open the Biweekly Mortgage Calculator →Frequently asked questions
- Why do 26 biweekly payments equal 13 monthly payments?
- Because there are 52 weeks in a year and you pay every two weeks, you make 52 / 2 = 26 half-payments annually. Twenty-six halves equal 13 whole payments, versus the 12 whole payments a standard monthly schedule collects. The 13th payment is the one extra payment that goes to principal each year.
- How much can biweekly payments save on a 30-year mortgage?
- On a $300,000 loan at 6.5%, biweekly payments cut roughly 5.8 years off the term and save about $88,000 in interest versus the standard schedule. The exact savings rise with a larger balance or higher rate - a $400,000 loan at 7.0% saves about $136,566 - so run your own loan through the calculator.
- Is paying 1/12 extra each month the same as biweekly?
- Nearly identical. Adding one-twelfth of your payment monthly contributes one extra payment a year, the same as biweekly. On a $300,000 / 6.5% loan the two methods differ by only about $865 in total interest over 24 years, which is a rounding error on a near-$300,000 interest bill.
- Does biweekly save money on its own, or only because of the extra payment?
- It saves only because of the extra payment landing on principal. Paying half every two weeks with no 13th payment would not shorten the loan meaningfully. The savings come entirely from that one extra full payment per year reducing principal, which lowers all future interest.
- How much is one extra payment per year in dollars?
- It is exactly one full monthly payment spread across the year. On a $1,896.20 monthly payment, you pay $1,896.20 extra over 12 months - which is one-twelfth ($158.02) added to each monthly payment, or the gap between 26 half-payments ($24,650.65) and 12 monthly payments ($22,754.45).
- Will biweekly payments lower my required monthly payment?
- No. Biweekly does not reduce your contractual payment - it accelerates payoff by adding principal. Your required payment stays the same, which is an advantage: if money gets tight you can revert to standard monthly payments without penalty, unlike a 15-year refinance that locks in a higher required payment.
Related guides
How to Calculate a Mortgage Payment, Step by Step · 15-Year vs 30-Year Mortgage: Which Should You Choose? · How Does Loan Interest Work? · How to Calculate a Car Loan Payment