U.S. mortgage planning
15 vs 30 year mortgage calculator.
Two loans, same balance. See the payment gap, the interest difference, and what return you would need on the monthly savings for the 30-year to come out ahead.
Your two loans
Short loan vs. long loan
Worked example
On a $400,000 loan with a 15-year rate of 6.00% and a 30-year rate of 6.50% (example inputs only, not current market rates), the 15-year payment is about $3,375 and the 30-year about $2,528, a gap of roughly $847 a month. Total interest is about $207,600 on the 15-year and about $510,200 on the 30-year. After 180 payments the 30-year loan still owes about $290,200, so $847 a month invested for 15 years would need to grow to that figure for the 30-year to break even: an average return of about 7.9% a year. Below that return, the 15-year loan leaves you ahead; above it, investing the difference does.
How the numbers work
Each payment uses the standard fixed-rate formula P = B × r / (1 − (1 + r)−n), with r the monthly rate (annual rate / 12) and n the number of monthly payments. The CFPB describes mortgage amortization the same way: early payments are mostly interest and the split shifts toward principal over time, and with a fixed-rate loan the combined principal and interest payment does not change (CFPB, fixed-rate mortgages). The CFPB also lists loan term, 30-year compared to 15-year, as a factor when you shop for a loan. Source pages checked 2026-09-30.
The break-even return is solved numerically: the monthly payment difference is invested at the end of each month for the shorter term at a monthly-compounded return, and the return is found where that balance equals the longer loan's remaining balance on the shorter loan's payoff date. No return and no rate is assumed; you enter the rates, and the optional return field only shows a result for your own figure. It ignores taxes on investment gains, the mortgage interest deduction, fees, and inflation.
FAQ
Is the 15-year loan always cheaper?
It has less total interest here because the term is shorter and the rate is usually lower, but the payment is higher. Whether it is better depends on what the monthly difference would otherwise earn and on your ability to keep paying it.
Why compare at the 15-year payoff date?
At that date the 15-year borrower owes nothing, so the 30-year borrower is ahead only if their invested savings exceed the balance still owed.
Does this include taxes, insurance or PMI?
No. It covers principal and interest only.
This tool is a planning estimate, not financial advice. Investment returns are not guaranteed.