Biweekly Mortgage Payment Calculator

Understanding the biweekly mortgage payment calculator — concept and principle

A biweekly plan replaces one monthly mortgage payment with half a payment every two weeks. Because a year has 52 weeks, you make 26 half-payments, the same as 13 monthly payments instead of 12. This calculator shows how much sooner the loan is paid off and how much interest you save.

How it is calculated

• Monthly payment a = P × i ÷ (1 − (1 + i)⁻ⁿ), with i = annual rate ÷ 12 and n = years × 12
• Interest, monthly plan = a × n − P
• Biweekly payment = a ÷ 2
• Biweekly plan: every two weeks, interest = balance × annual rate ÷ 26 is added and a ÷ 2 is subtracted, until the balance reaches zero. Payoff time = number of payments ÷ 26 years.
• Interest saved = monthly-plan interest − biweekly-plan interest

The principle

The saving comes almost entirely from the extra 13th payment each year, and all of it goes to principal. A lower balance means less interest next period, so more of each later payment also goes to principal, and the effect snowballs. A small part of the gain in this model also comes from paying a little earlier in each month. Many lenders only apply the money once a month, so their real result is slightly smaller than shown.

Worked example

1. Loan $300,000 at 6% for 30 years, so i = 0.005 and n = 360.
2. Monthly payment = 300,000 × 0.005 ÷ (1 − 1.005⁻³⁶⁰) ≈ $1,798.65; interest over 30 years ≈ $347,514.57.
3. Biweekly payment = 1,798.65 ÷ 2 ≈ $899.33, with interest of 6% ÷ 26 per period.
4. The balance reaches zero after 638 payments: 638 ÷ 26 ≈ 24.5 years.
5. Interest on the biweekly plan ≈ $273,078.55, so interest saved ≈ $74,436.02, and time saved is 5 years 6 months.

How to read the result

Savings are larger for long terms and high rates, and small for short loans. You can get a very similar result by adding one-twelfth of a payment to every monthly payment, with no special program. Compare any setup fee against the interest saved, and weigh paying extra on a mortgage against other uses of the money, such as clearing more expensive debt or building an emergency fund.

Common mistakes

• Paying a fee for a biweekly service that simply holds the money until month-end.
• Assuming the lender applies extra money to principal without checking.
• Thinking biweekly means twice a month; 24 semi-monthly payments give no extra payment.

Frequently asked questions

How much faster is a 30-year loan paid off biweekly?

At around 6%, roughly five to six years sooner. The exact gain depends on the rate and the lender's crediting method.

Is it better than making one extra payment a year?

The total extra paid is the same. Biweekly spreads it out and applies it slightly earlier, so it saves a little more.

Does it work for other loans?

Yes, the same logic applies to any amortising loan that allows prepayment without penalty.

Sources: Standard time value of money mathematics (loan amortisation) · Consumer Financial Protection Bureau (CFPB), guidance on mortgage prepayment