15-Year vs 30-Year Mortgage Calculator

How it works

A 15-year and a 30-year loan on the same amount differ in two ways: the shorter term usually carries a lower rate, and it packs the payments into half the time. Both the payment and the lifetime interest come from the standard amortization, where interest is simply every payment added up minus the amount borrowed:

With the defaults above, a $320,000 loan at 6.3% over 15 years has a payment of about $2,752 and racks up roughly $175,447 in interest. The same loan at 7% over 30 years pays about $2,129 a month but about $446,428 in interest. So the 15-year costs several hundred dollars more each month yet saves around $270,982 over the life of the loan.

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A worked example: $320,000, 15-year vs 30-year

Two buyers take the same $320,000 loan. One picks a 15-year term at 6.3%, the other a 30-year at 7%. Over the life of the loan, the 15-year borrower saves $270,982 in interest.

The trade-off shows up in the monthly payment. The 15-year runs $2,752 a month against $2,129 for the 30-year, so you commit an extra $624 every month. In exchange, total interest drops from $446,428 on the long loan to $175,447 on the short one.

So the shorter term costs more now and far less overall, while the longer term keeps your monthly obligation lower and your cash freer. Enter your own loan amount and both rates to see which side of that $624 gap fits your budget.

Which term fits you

• Choose 15-year if the payment fits comfortably. It is the cheapest way to own outright, with a lower rate and a fraction of the interest, and it forces disciplined payoff.
• Choose 30-year for flexibility. The lower required payment leaves room for emergencies, investing, or other goals, and you can always pay extra to mimic a shorter term.
• Consider the middle path. Many buyers take the 30-year for its safety net and voluntarily pay more when they can, keeping the option to fall back on the smaller payment.

Why the 15-year payment is not double

Cutting the term in half does not double the payment, which catches many buyers off guard. A 15-year payment typically runs only 25% to 40% higher than a 30-year on the same loan, not 100% higher. Two things soften the blow: the shorter loan usually carries a lower rate, and packing principal into fewer years is partly offset by the far smaller interest bill.

The exact gap for your numbers shows in the breakdown above.

• Less interest to spread. A 15-year loan accrues interest for half as long, so a big chunk of what stretches the 30-year payment out simply is not there.
• A lower rate helps. Lenders reward the shorter commitment with a better rate, trimming the payment gap further.
• More principal per payment. The higher payment is mostly principal from day one, which is why equity in a 15-year loan builds so quickly.
• Total cash out is lower. Even though each 15-year payment is bigger, you make half as many of them, so the sum handed over across the loan is far smaller.

What the interest gap really buys

The 15-year loan’s headline appeal is the enormous interest saving, but that saving is not free money, it is the payoff for committing a larger payment for 15 years. Whether it is the best move depends on what you would otherwise do with the difference between the two payments each month.

• Guaranteed saving. Choosing the 15-year locks in the lower lifetime interest with certainty, a risk-free return equal to the loan’s rate.
• Opportunity cost. The extra you pay each month is money you cannot invest elsewhere, so a strong long-run investor might come out ahead with the 30-year and the difference invested.
• Behavior matters. The 15-year forces the saving, while the invest-the-difference plan only works if you actually invest it rather than spend it.
• Rates tilt the call. When mortgage rates are high, the guaranteed saving from the 15-year is harder for investments to beat; when they are low, the 30-year looks better.

Qualifying and the flexibility trade-off

The two terms also differ in how they interact with your budget and your loan approval, not just the total cost. Because a 15-year demands a bigger monthly payment, it uses up more of your borrowing capacity, so it is worth weighing the payment you must make against the payment you would choose to make.

• Debt-to-income. The higher 15-year payment pushes up your debt-to-income ratio, so you may qualify for a smaller loan than the 30-year would allow.
• The safety net. The 30-year’s lower required payment leaves room to breathe if income drops, since you are never obligated to pay more than that amount.
• A middle path. Many buyers take the 30-year for its low floor, then pay extra to mimic a 15-year, keeping the option to ease off whenever they need to.