15-Year vs. 30-Year Mortgage: The Real Cost Difference
By the SteadyCalc team · Updated July 16, 2026
A 15-year and a 30-year mortgage can finance the exact same house and still produce wildly different outcomes. Below is one $320,000 loan run both ways — monthly payment, total interest, and equity after five years — plus an honest look at when each term makes sense.
The same loan, two ways
To keep the comparison fair, we'll run a single loan amount through both terms: $320,000, roughly what you'd finance on a $400,000 home with 20% down. Say the 30-year quote is 6.5% and the 15-year is 5.9%. Those are assumptions, not current market rates, but the gap between them is realistic — 15-year rates typically run lower because the lender's money is exposed for half as long.
At those rates, the 30-year loan costs about $2,023 a month in principal and interest. The 15-year costs about $2,683. That $660 monthly difference is the entire decision, compressed into one number. Everything below is really a question of what that $660 is worth to you: lower lifetime cost, or breathing room in your budget every single month for fifteen years. You can rerun this comparison with your own numbers in our mortgage calculator by changing only the term field.
The numbers side by side
Here is the full picture, with figures rounded to the nearest dollar:
| 30-year at 6.5% | 15-year at 5.9% | |
|---|---|---|
| Monthly principal & interest | $2,023 | $2,683 |
| Total interest paid | $408,142 | $162,955 |
| Total paid over the loan | $728,142 | $482,955 |
| Balance remaining after 5 years | $299,555 | $242,771 |
Read that middle row twice. The 30-year loan costs about $245,000 more in interest — on a $320,000 loan, you pay back more in interest than you borrowed in the first place. The 15-year borrower pays interest too, about $163,000 of it, but walks away owning the house 15 years sooner having paid roughly $245,000 less for the privilege.
The five-year row matters because most people never hold a mortgage to term. Suppose you sell at the five-year mark. The 30-year borrower has written checks totaling about $121,400 and converted roughly $20,400 of that into equity — the other $100,900 went to interest. Over the same stretch, the 15-year borrower paid in about $161,000 but banked roughly $77,200 of it as principal, losing only about $83,800 to interest. Despite the smaller checks, the 30-year borrower actually paid more interest in those five years, and kept far less of the money.
Why the 15-year builds equity so much faster
Look at the bottom row of the table. Five years in, the 30-year borrower has paid the balance down by about $20,400. The 15-year borrower has paid down about $77,200 — nearly four times as much principal, despite paying only about 33% more per month.
That lopsided result comes from how amortization splits each payment. In month one of the 30-year loan, interest claims about $1,733 of the $2,023 payment, leaving just $289 for principal. On the 15-year loan, interest takes about $1,573 of the $2,683 payment — both loans start with a similar interest bill, because the balance is the same — but $1,110 goes to principal. Every extra dollar in the 15-year payment attacks the balance directly, which shrinks next month's interest charge, which frees even more of the following payment for principal. The mechanics are worth understanding on their own; our guide to how amortization works walks through them step by step.
Equity is the practical payoff. It's what you keep if you sell, what you can borrow against, and what determines when PMI can come off if you put down less than 20%.
Taking the 30-year and paying it like a 15
A popular middle path: take the 30-year for its lower required payment, then voluntarily add the $660 difference as extra principal each month. It works better than you might expect. On our example loan, sending $2,683 a month to the 30-year pays it off in 193 months — about 16 years — and cuts total interest to roughly $196,000. That is about $212,000 less than riding the 30-year to the end.
Two catches, though. First, the higher 30-year rate never goes away, so this strategy still costs about $33,000 more in interest than the true 15-year loan at 5.9%. You are paying roughly 0.6 percentage points extra for the option to stop making the bigger payment. Second, the whole plan runs on discipline. The bank will happily accept $2,023 forever, and life will supply reasons to skip the extra $660 — a car repair this month, a vacation the next. Borrowers who choose the 15-year are contractually locked into the payoff. Borrowers who plan to prepay a 30-year are relying on future selves who may have other ideas.
The case for investing the difference instead
Flip the strategy around: take the 30-year and invest the $660 a month rather than prepaying. Suppose those investments return 7% a year — an assumption, and far from guaranteed. After 15 years of monthly contributions, you'd have roughly $209,000, of which only about $119,000 was money you put in. If markets cooperate, that stack can outgrow the interest you'd have saved by prepaying a 6.5% loan.
Notice the trade you're making, though. Prepaying the mortgage earns you a guaranteed, tax-free return equal to your loan rate; investing offers a higher expected return with real risk attached, including years where the market drops while your mortgage interest accrues on schedule. Order of operations matters here too — a 401(k) employer match is an instant return no mortgage strategy can touch, so capture that before committing spare cash to either side of this debate.
Who each term genuinely fits
The right answer usually falls out of your cash flow, not the interest math.
- The 30-year fits you if the 15-year payment would leave you with a thin margin after essentials, you carry higher-rate debt like credit cards or a car loan, you haven't yet filled your emergency fund, or you aren't capturing your full employer retirement match. A mortgage at 6.5% is cheap debt next to a card at 22% — aim the extra $660 at the expensive balance first.
- The 15-year fits you if the higher payment sits comfortably inside your budget with room to spare, your income is stable, retirement savings are on track, and a paid-off house by a specific date — say, before the kids hit college or before you retire — matters to you more than portfolio upside.
Lenders will also qualify you differently: the 15-year's bigger payment counts against your debt-to-income ratio, so it can shrink the price range you're approved for.
A practical stress test before you commit: live on your budget for three months as if the 15-year payment were already due, moving the $660 difference into savings each month. If that feels tight in a normal month, picture it in a month with a transmission repair or a layoff scare. What the 30-year really sells is a lower mandatory payment — you keep the choice, every month, of whether to top it up.
You can switch later, but only one direction is free
Choosing the 30-year keeps your options open at no cost: you can always pay extra, stop, and start again. Moving the other way is harder. If you take the 15-year and the payment later becomes a strain, your escape route is refinancing into a longer term, which means closing costs and whatever rates happen to be at that moment. Many people do the reverse on purpose — start with a 30-year, then refinance into a 15-year once income grows or rates dip. Our refinance calculator shows the break-even point on that move, including closing costs.
Frequently asked questions
Why are 15-year mortgage rates lower than 30-year rates?+
Lenders price risk over time. A 15-year loan returns the lender's money twice as fast, which means less exposure to inflation, rate changes, and the chance of default over the decades. That shorter risk window usually translates into a meaningfully lower rate than the same borrower would get on a 30-year loan.
Can I pay off a 30-year mortgage in 15 years?+
Yes. Add the payment difference as extra principal each month and the loan retires in roughly 16 years in our example. Confirm your loan has no prepayment penalty and that extra payments are applied to principal, not held for the next installment. You will still pay somewhat more interest than a true 15-year because of the higher rate.
Is the 15-year mortgage always the cheaper choice?+
It is almost always cheaper in total interest, but that is not the whole picture. If the bigger payment forces you to skip retirement contributions, carry credit card balances, or drain your emergency fund, the interest you save can cost you more elsewhere. Cheapest on paper and best for your situation are different questions.
Does the size of my down payment change this comparison?+
The ratios hold at any loan size: the 15-year still builds equity dramatically faster and cuts total interest by a similar proportion. A larger down payment shrinks both payments and, once you reach 20% down, removes PMI on conventional loans, which lowers the monthly cost of either term.
What if I want the 15-year but can't quite afford the payment?+
Take the 30-year and prepay what you can, even if it is less than the full difference. Any consistent extra principal shortens the loan and cuts interest. Revisit refinancing into a 15-year later if your income rises or rates fall enough to cover the closing costs.
Keep going
Why early loan payments are mostly interest, how the balance actually falls each month, and what extra principal payments really do.
How the two payoff methods differ, what the interest gap looks like in real dollars, and how to pick the one you will actually stick with.
Estimate your monthly mortgage payment including principal, interest, and a full amortization schedule.
Compare your current mortgage payment to a new rate and term, and find the break-even point on your closing costs.