Biweekly Mortgage Savings Calculator

Biweekly mortgage payments work by splitting your standard monthly payment in half and paying that amount every two weeks instead of once a month. The whole effect comes from a calendar fact: there are 26 biweekly periods in a year, which is 13 full monthly payments rather than 12. That thirteenth payment goes entirely to principal.

Which biweekly are you actually being offered? This matters more than most articles admit, because the two arrangements go by the same name and do not save the same amount.

This page models a true biweekly loan: interest accrues fortnightly and each half-payment reduces the balance the day it lands. That is the accelerated biweekly arrangement Canadian lenders sell, and what a handful of US lenders will write.

The far more common US product is a biweekly payment program bolted onto an ordinary monthly loan. The servicer collects your half-payments, holds them, and applies one extra full payment once a year. The balance only moves twelve times a year plus that lump. The biweekly vs monthly payment calculator models that one.

On a $300,000 loan at 6.5% over 30 years the true biweekly saves about $88,100 and the hold-and-apply program about $84,000. Both cut roughly five years and nine months off the term, so the difference is real but not enormous. Ask your servicer which one they run before you pay anyone a setup fee for it.

Standard monthly payment formula: M = P × [r(1+r)^n] ÷ [(1+r)^n − 1]

Where:

• M = monthly payment amount
• P = principal (loan amount)
• r = monthly interest rate = annual rate ÷ 12
• n = total number of monthly payments (years × 12)

Biweekly payment: Biweekly Amount = M ÷ 2

Annual extra payment: Extra Principal/Year = M × 1 (one full extra monthly payment)

There is no clean closed-form shortcut for the saving. Every extra dollar of principal removes all the future interest that dollar would have carried, and how much that is depends on when in the schedule it lands. The calculator simulates each of the 26 payments a year against the declining balance, which is the only way to get it right.

What each variable means:

• Principal: the original loan amount, or current outstanding balance
• Annual Interest Rate: your mortgage’s stated rate, not the APR (Annual Percentage Rate), which folds the fees in and so runs higher
• Loan Term: typically 15 or 30 years; the calculator models full or remaining term
• Extra payment impact: the extra annual payment reduces the balance earlier, meaning subsequent interest charges are calculated on a lower base

Reference: typical savings on a 30-year mortgage at 7%

• $200,000 loan: saves about $68,900 in interest, pays off 6.3 years early
• $350,000 loan: saves about $120,600 in interest, pays off 6.3 years early
• $500,000 loan: saves about $172,300 in interest, pays off 6.3 years early

Notice that the years saved is identical across all three. It has to be: the payoff date depends only on the rate and the term, not on the size of the loan. Double the balance and you double the interest saved, but the finish line moves by exactly the same amount.

Worked example: Loan: $350,000. Rate: 6.5%. Term: 30 years.

Monthly payment = $350,000 × [0.005417 × (1.005417)^360] ÷ [(1.005417)^360 − 1] = $2,212.24/month

Biweekly payment = $2,212.24 ÷ 2 = $1,106.12 every two weeks

Over a year that is 26 payments, or $28,759 against the $26,547 you would pay monthly. The extra $2,212 goes entirely to principal, and because it lands earlier every year the effect compounds.

Interest paid monthly: $446,406 Interest paid biweekly: $343,597 Interest saved: $102,809 Loan paid off in 24.2 years instead of 30, so 5.8 years early.

The saving is far larger than most people expect, and larger than the “about $60,000” figure that gets quoted around the web for a loan this size. One extra payment a year does not sound like much. Applied straight to principal for two decades, it is.