15-Year vs 30-Year Mortgage: The Real Trade-Off

On a $300,000 loan, a 15-year mortgage saves you roughly $226,950 in interest compared with a 30-year. That single number makes the choice look obvious. It is not, and the reason is worth understanding before you commit for a decade and a half.

The two loans side by side

Fifteen-year mortgages carry lower rates than thirty-year ones - typically 0.5 to 0.75 percentage points less, because the lender's money is at risk for half as long.

	30-year at 6.5%	15-year at 6.0%
Monthly principal & interest	$1,896	$2,532
Total interest	$382,633	$155,683
Total repaid	$682,633	$455,683
Interest as % of loan	128%	52%

The 15-year costs $636 more a month and saves $226,950. Run your own figures in the mortgage calculator by switching the term.

Why the saving is so large

Two effects compound. The lower rate helps, but the bigger factor is time: interest accrues on the outstanding balance every month, so halving the number of months roughly halves the exposure.

The difference shows in how fast you build equity:

After	30-year balance	15-year balance
5 years	$280,924	$224,443
10 years	$254,523	$130,652
15 years	$217,776	$0

At the ten-year mark the 15-year borrower owes $123,871 less. If you sell at that point, that is the difference in cash you walk away with.

The case against, which is stronger than it looks

The payment is not optional. This is the real risk. $636 a month is a commitment for 180 months. Lose your job in year three and the 30-year payment is far easier to cover. A 30-year borrower who chooses to pay extra can stop any month; a 15-year borrower cannot.

It reduces how much house you qualify for. Lenders assess the actual payment, so the same income supports a smaller loan on a 15-year term - often 20-25% less.

The money might work harder elsewhere. This is the argument that carries the most weight. Investing the $636 difference for 15 years at a 7% return produces roughly $202,000. Against $226,950 of interest saved, the mortgage wins - but not by the landslide the headline suggests, and at 8% the two are close to even.

Test the comparison in the compound interest calculator.

Employer match beats both. If you are not capturing your full 401(k) match, that is an immediate 50-100% return. Doing that before accelerating a 6% mortgage is not a close call.

The middle path most people miss

Take the 30-year, then voluntarily pay it like a shorter loan.

Paying an extra $636 a month on the 30-year at 6.5% clears it in about 17 years 2 months with roughly $186,000 of interest. That is $30,000 worse than a true 15-year - the cost of the higher rate - but you keep the right to drop back to $1,896 in any month you need to.

For most people, $30,000 over seventeen years is a fair price for that flexibility. For someone with very stable income and a healthy emergency fund, the 15-year's lower rate is the better deal.

How to decide

A 15-year makes sense if the payment is comfortably affordable, you have 6+ months of expenses saved, you are capturing your full employer match, and your income is stable.

A 30-year makes sense if the higher payment would stretch you, your income varies, you have higher-interest debt to clear first, or you want the option to invest instead.

Take the 30-year and overpay if you want most of the saving while keeping the escape hatch. This suits more people than either pure option.

One caution: if you choose the 30-year intending to overpay, set up the extra payment automatically. The interest saving only materialises if the extra payment actually happens every month, and intentions decay.

Estimates for general information only, not financial advice. Rates and terms vary by lender and credit profile.