Biweekly Mortgage Calculator
Compare a standard monthly mortgage with a biweekly payment plan and see how much time and interest you save.
Time saved with biweekly payments
5.8 years
- Standard monthly payment (P&I)
- £1,580.17
- Biweekly payment
- £790.09
- Loan paid off in
- 24.2 years
- Total interest — monthly schedule
- £318,861.22
- Total interest — biweekly schedule
- £246,147.00
- Total interest saved
- £72,714.22
Paying half the monthly P&I every two weeks means 26 cheques a year — the equivalent of 13 monthly payments instead of 12. That extra payment goes straight to principal each year, shrinking the balance faster and cutting roughly five to seven years and tens of thousands of dollars in interest off a typical 30-year mortgage.
How to use this calculator
Enter the loan amount, your annual interest rate (APR), and the loan term in years (most US mortgages are 15 or 30). The calculator returns the standard monthly principal-and-interest payment, the equivalent biweekly payment (half the monthly amount), the new payoff term, and the total interest you save by switching to a true biweekly schedule.
How the calculation works
A true biweekly mortgage pays half the standard monthly principal-and-interest amount every two weeks. Because there are 26 fortnights in a year — not 24 — the borrower makes the equivalent of 13 monthly payments per year instead of 12. That extra full payment each year goes straight to principal. The maths is closed-form: starting from the standard amortisation payment M = L × r / (1 − (1+r)^−n), the effective monthly payment under the biweekly plan is M_eff = M × 13/12, and the new payoff term in months is k = −ln(1 − L·r / M_eff) / ln(1+r). Because principal shrinks faster, every future month accrues less interest — that compounds and is why a 30-year loan typically finishes in roughly 24 years under a biweekly plan.
Worked example
A 250,000 dollar mortgage at 6.5% APR over 30 years has a standard monthly payment of about 1,580 dollars and accrues about 318,860 dollars in total interest. The equivalent biweekly payment is 790 dollars every two weeks. Under that schedule the loan is fully repaid in about 24 years 2 months — roughly 5.8 years earlier — and total interest falls to about 246,440 dollars. That is a saving of roughly 72,420 dollars over the life of the loan, with no change to monthly cash flow on average.
Frequently asked questions
How does a biweekly mortgage save so much interest?
There are 52 weeks in a year, which is 26 fortnights. Half the monthly payment, paid 26 times, equals 13 full monthly payments — one more than a standard schedule of 12 monthly payments per year. That extra full payment is applied entirely to principal each year. Because mortgage interest is charged monthly on the outstanding balance, every dollar of principal paid down today saves all the interest that balance would have accrued for the rest of the loan. Compounded over decades, that single extra annual payment removes tens of thousands of dollars in interest from a typical 30-year mortgage and cuts the term by five to seven years.
Will my lender actually accept biweekly payments?
Most US lenders and servicers accept biweekly payments, but the way they apply them varies. A true biweekly plan posts half the monthly payment every two weeks and applies the funds immediately to principal each fortnight — this is the schedule the calculator models. Some servicers instead hold the half-payments in a suspense account and only apply them once the full monthly payment has accumulated, which gives you the 13-payments-a-year benefit but not the additional interest savings from twice-monthly application. Third-party "biweekly plan" providers also exist, but they typically charge an enrollment fee and offer no benefit you cannot get for free. Before signing up, call your servicer and ask exactly how biweekly payments are applied.
Are there fees or downsides to a biweekly mortgage?
A genuine biweekly plan offered directly by your servicer is usually free. Third-party setup services can charge 200 to 400 dollars to enroll plus monthly fees — money you could have applied to principal instead. The other consideration is liquidity: an extra payment each year goes into the house, where you cannot easily get it back without a refinance or home equity loan. If you do not have a 3-to-6-month emergency fund or are carrying high-interest unsecured debt, those should be cleared first. Finally, on a mortgage with a prepayment penalty — rare on owner-occupied US loans originated after January 2014, but still found on some non-QM and investment-property mortgages — check the note before accelerating payments.
Is it better to do biweekly payments or just add extra to my monthly payment?
Mathematically the two strategies are nearly identical. Biweekly payments of half the monthly amount on a true biweekly schedule produce the same effective extra payment as adding one-twelfth of the monthly P&I to each monthly payment. The choice is operational: biweekly works well if you are paid every two weeks because each cheque covers the same payment; adding one-twelfth to each monthly payment is simpler if your income arrives monthly. Both beat the standard 12-payment schedule. If you want to model the "add extra each month" version, use the Mortgage Payoff Calculator with the extra-payment field set to roughly monthly_payment / 12.
Does this work the same for 15-year and 30-year mortgages?
Yes — the maths is identical, but the relative saving is larger for longer loans. A 30-year mortgage has decades of interest still to accrue, so accelerating principal repayment removes a lot of future interest. A 15-year mortgage is already amortising faster and carries less interest in absolute terms, so biweekly payments still help but the headline saving will be smaller — typically one to two years off the term and a few thousand dollars in interest rather than the five to seven years and tens of thousands saved on a 30-year loan.
Should I refinance to a 15-year mortgage instead of doing biweekly on a 30-year?
It depends on your cash flow and rate environment. Refinancing to a 15-year mortgage typically gets you a lower interest rate (15-year rates are 0.25 to 0.75 percentage points below 30-year rates on average) but commits you to a much higher mandatory monthly payment. Switching to biweekly on a 30-year keeps the lower mandatory payment and lets you pause the extra payments if your income changes. As a rule of thumb: refinance to 15-year if you are confident in your income and want the lower rate; stay 30-year + biweekly if you want flexibility. This calculator only models the biweekly-on-existing-loan path — for refinance maths, see the Refinance Calculator.