Is a 15-year mortgage worth the bigger payment? The 15 vs 30-year mortgage calculator compares the two loans side by side. It uses Freddie Mac's average rates for the week of October 15, 2026: 6.71% for a 15-year fixed loan and 7.4% for a 30-year.
Its default loan is $334,000, which is 80% of the $417,500 median existing-home price the National Association of Realtors reported for September 2026. On that loan, the 15-year mortgage costs $2,948 a month and the 30-year costs $2,313. The shorter loan costs $636 more each month, about 27% more. In return, it saves $301,842 in interest and ends 15 years sooner.
The two loans side by side
| On $334,000 | 15-year | 30-year |
|---|---|---|
| Rate | 6.71% | 7.4% |
| Monthly payment | $2,948 | $2,313 |
| Total interest | $196,675 | $498,517 |
| Total paid | $530,675 | $832,517 |
These payments cover principal and interest only. Property tax, insurance and any mortgage insurance come on top of both.
The savings come from two places: a lower rate, and half as many years of interest. Equity also builds much faster. After five years, the 15-year borrower owes $257,216, against $315,707 on the 30-year loan. After 15 years, the shorter loan is paid off. The 30-year borrower still owes $250,999 of the original $334,000, because early payments go mostly to interest.
What if you invest the difference?
The case for the 30-year loan is flexibility, and the chance to invest the money a lower payment frees up. The calculator tests that idea. Both borrowers spend $2,948 a month for 30 years. The 15-year borrower pays off the house, then invests the whole payment for the last 15 years. The 30-year borrower invests the $636 difference from the first month.
At the default 6% yearly return, the 15-year plan has $845,872 invested by year 30. The 30-year plan has $619,446. The 15-year borrower comes out ahead by $226,426.
Investing the difference only wins if it earns more than about 9% a year (8.99% in the calculator) after taxes and fees. It has to do that every year, through downturns, and you have to actually invest the money.
Paying a 30-year loan like a 15-year
There is a middle path: take the 30-year loan, but pay the 15-year amount anyway. Paying $2,948 a month on the $334,000 30-year loan at 7.4% clears it in about 16.3 years, with $241,174 of interest. That is more than the true 15-year loan costs, because the rate is higher. In exchange, the required payment stays at $2,313, so you can drop back to it in a tight month. The page suggests checking that your lender applies extra payments to principal and charges no prepayment penalty.
The cost in buying power
A bigger payment also means a smaller budget. On the Points Frog home affordability calculator, a household earning $100,000 with $40,000 down and $500 of monthly debts could afford about $309,000 with a 30-year loan at 7.4%. With a 15-year loan at 6.71%, the same budget buys only about $260,000.
How loan size changes the gap
At the same rates, the gap grows in step with the loan:
| Loan | 30-year payment | 15-year payment | Interest saved |
|---|---|---|---|
| $200,000 | $1,385 | $1,765 | $180,744 |
| $300,000 | $2,077 | $2,648 | $271,116 |
| $400,000 | $2,770 | $3,531 | $361,488 |
| $500,000 | $3,462 | $4,413 | $451,860 |
What the calculator leaves out
It compares principal and interest on fixed-rate loans. Property tax, insurance and mortgage insurance are the same either way, so they are left out. So are closing costs, any mortgage interest deduction and the chance that you sell or refinance early. In the investing test, returns compound monthly, before any tax. Your own rates depend on your credit, down payment and lender. As the page puts it, if you can comfortably afford the higher payment and still save for retirement and emergencies, the 15-year loan saves a lot of interest and leaves you debt-free sooner.
Where the figures come from
The rates are Freddie Mac's Primary Mortgage Market Survey averages for the week of October 15, 2026, read from FRED. Fifteen-year rates usually run lower because a lender's money is tied up for less time. The default loan is 80% of the National Association of Realtors' September 2026 median existing-home price.
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Source: Freddie Mac via FRED, week of October 15, 2026; National Association of Realtors, September 2026. Figures are educational estimates, not financial advice.