Home & mortgage

15-Year vs. 30-Year Mortgage Calculator

Compare the lower payment of a 30-year mortgage with the faster payoff and lower lifetime interest of a 15-year mortgage—and test the common “invest the payment difference” argument.

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Your mortgage comparison

The sample values are calculated automatically. Change the assumptions to see your own estimate.

These calculators provide mathematical planning estimates, not financial, tax, legal, or investment advice. Actual rates, returns, fees, taxes, market values, and lender practices can change the result.

Understand the result

There are really two comparisons

The first comparison is contractual: payment size and lifetime interest. A 15-year loan usually requires a larger monthly payment but pays principal down much faster.

The second comparison is behavioral: what happens if the borrower choosing the lower 30-year payment actually invests the difference every month? The calculator also gives the 15-year borrower credit for investing the former mortgage payment after that loan is paid off.

Equal-cash-budget assumption

Years 1–15: 30-year borrower invests the payment difference.
Years 16–30: 15-year borrower invests the full former 15-year payment.
Both investment accounts use the same return assumption.
Taxes, investment fees, and refinance behavior are excluded.

Want to model extra mortgage payments?

Use the free Mortgage Payoff Calculator online, or the Windows version to save plans and edit individual months.

Open Mortgage Payoff Calculator

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Frequently asked questions

Why can the 30-year strategy sometimes look better in the investment comparison?

Because the lower monthly payment can free cash for investment over a long period. That outcome depends on actually investing the difference and earning the assumed return.

Is mortgage interest savings guaranteed?

If the loan remains in place and payments are made as scheduled, the contractual interest difference is much more certain than a market-investment return.

Does the calculator include taxes and insurance?

No. Those costs are generally independent of whether the mortgage term is 15 or 30 years, so this calculator focuses on principal, interest, and investment opportunity cost.