Financial Calculators

15-year vs 30-year mortgage — true cost comparison

See the monthly payment + total interest for both terms side by side.

15-Year vs 30-Year Mortgage Calculator

Table of contents

◦15-Year vs 30-Year Mortgage
◦Formula
◦How to use
◦Worked example
◦FAQ

15-Year vs 30-Year Mortgage

The 15-year mortgage costs more per month but far less in total interest. The 30-year is cheaper monthly but you pay 2–3× as much interest over the life of the loan.

This calculator shows both side-by-side for the same loan amount and rate so you can decide which works for your cash flow vs. your long-term cost.

Formula

Monthly payment uses the standard mortgage amortization formula:

M = P × r / (1 − (1 + r)<sup>−n</sup>)

Where:

  • P = principal (loan amount)
  • r = monthly interest rate (annual rate ÷ 12 ÷ 100)
  • n = total payments (180 for 15-year, 360 for 30-year)

Total interest = monthly payment × n − principal.

How to use

  1. Enter the loan amount — the principal you'll finance.
  2. Enter the annual rate as a percent (e.g. 6.5 for 6.5%).

The calculator instantly shows monthly payments for both terms, total interest for each, and the head-to-head delta.

Worked example

$400,000 loan at 6.5%:

  • 15-year monthly payment: $3,485
  • 30-year monthly payment: $2,528
  • Monthly difference: $957 more for the 15-year
  • 15-year total interest: $227,277
  • 30-year total interest: $510,178
  • Interest saved by the 15-year: $282,901

You pay an extra $957/month for 15 years (180 × $957 = class="jsx-43013d48d08af43a site-content "72,260) — but save $282,901 in total interest. Net: paying off in 15 years saves you about class="jsx-43013d48d08af43a site-content "10,640 even after accounting for the higher payments.

FAQ

Are 15-year rates lower than 30-year rates?

Almost always — typically 0.5 to 0.75 percentage points lower. This calculator assumes the same rate for both for an apples-to-apples comparison; in reality the 15-year is even more advantageous than this shows.

What if I take a 30-year and just pay extra?

You can! Prepaying a 30-year to match a 15-year amortization yields almost the same total interest. The advantage is flexibility — you keep the option to make smaller payments in lean months.

Why not 20-year mortgages?

Some lenders offer them; the math is the same with n=240 payments. The 15/30 comparison is the industry standard.

What's not in this calculation?

Property tax, homeowner's insurance, PMI (if applicable), HOA fees, and closing costs. This is purely the principal-and-interest comparison. Your total monthly housing cost will be higher.