15-year vs 30-year mortgage: which saves more?

The 30-year fixed is the default American mortgage for a reason: predictable payment, long horizon, manageable monthly cost. But the 15-year alternative cuts the interest you'll pay by more than half on the same loan. The right choice depends on what you're actually optimizing for — and there's a third option most buyers don't realize exists.

The headline numbers

Take a $400,000 loan at the typical 2026 spread (30-year at 7.0%, 15-year at 6.25%):

• 30-year, 7.0%: monthly P&I = $2,661. Total interest over 30 years = $558,000
• 15-year, 6.25%: monthly P&I = $3,429. Total interest over 15 years = $217,000

The 15-year saves you roughly $341,000 in total interest — the price of another house. The cost is an extra $768 per month for 15 years.

Run your own scenario in the mortgage calculator to see exact numbers for your loan size and rate.

The case for the 15-year

• Massively less total interest. The compounding works in your favor — you pay down principal twice as fast.
• Lower rate. 15-year rates are almost always 0.5–0.75 points below 30-year rates because the lender's risk window is shorter.
• Forced equity-building. You're done in 15 years. The discipline of a higher payment can be a feature, not a bug.
• Faster path to PMI removal. You hit 20% equity quickly and stop paying PMI.

The case for the 30-year

• Lower required payment. $768 less per month on our example is real money. That's an extra retirement contribution, an emergency fund, or a family vacation.
• Flexibility. If you lose income, get sick, or face an unexpected expense, the lower required payment is a buffer the 15-year can't give you.
• Opportunity cost. If you can earn more than your mortgage rate (after tax) by investing the difference, the math favors the 30-year. Historically, S&P 500 returns have outpaced 6–7% mortgage rates over long periods, though never guaranteed.
• Tax treatment. Mortgage interest is sometimes deductible (if you itemize), which slightly favors the higher-interest 30-year.

The third option: a 30-year with extra payments

Here's the move most buyers don't realize is available: take the 30-year, but voluntarily pay extra principal every month. You get most of the interest savings of a 15-year while keeping the safety net of a lower required payment.

On our $400,000 / 7% / 30-year example, paying an extra $768/month (the difference between the 15-year and 30-year payments) pays the loan off in about 16.5 years and saves around $320,000 in total interest. Not quite the 15-year, but close — and if you ever need to drop back to the regular $2,661 payment, you can, without refinancing.

The downside: you don't get the lower 15-year rate. You're paying 7% on the 30-year vs 6.25% on the 15-year. That extra 0.75% costs roughly $40,000 over the accelerated payoff period in our example. So the 15-year still wins on pure dollar count — but the flexibility difference is meaningful.

Which is right for you?

A useful test: if you can comfortably afford the 15-year payment AND fully fund retirement AND maintain a 3–6 month emergency fund AND not feel financially pinched, take the 15-year. The pure interest savings are too large to ignore.

If the 15-year payment would crowd out retirement contributions, eat your emergency fund, or leave no room for life happening, take the 30-year — and pay extra principal voluntarily whenever you can.

If you're somewhere in between, the 30-year with consistent extra payments is the lowest-regret choice.

One thing the calculator can't tell you

Behavior matters more than math. Lots of borrowers take the 30-year intending to make extra payments and... don't. If you know yourself well enough to know the 15-year's forced discipline is the only way you'll actually pay extra, that's a valid reason to choose it. Conversely, if you're a disciplined saver who'd genuinely invest the difference, the 30-year-plus-investing path may beat the 15-year over a long horizon.

Try it yourself

Plug both terms into the mortgage calculator with your real numbers. Then add an "extra monthly payment" to the 30-year scenario equal to the difference between the two monthly payments. The three numbers you'll see — pure 30-year, pure 15-year, and 30-year-with-extras — frame the actual decision better than any rule of thumb.