15 Year vs 30 Year Mortgage Calculator

All figures below are for a $400,000 loan, computed with the amortization engine on this site. The 30-year rate is 6.5% and the 15-year rate 5.75%, reflecting the rate discount shorter terms normally carry; the third column uses the 30-year rate with the payment difference added as voluntary extra principal from month one.

Three things fall out of this table that the usual two-column version hides.

The 15-year genuinely wins on cost. $197,895 against $249,555 is a real $51,660 advantage over the disciplined 30-year, and it comes almost entirely from the rate discount rather than the term. Run both at the same 6.5% and the 15-year costs $227,197 — the gap narrows to $22,358. Most of what a 15-year mortgage buys you is a cheaper rate, not a shorter schedule.

The payment difference is larger in proportion than it sounds. $793.37 is a 31% increase in the mandatory monthly obligation. Lenders qualify you against the higher figure, so a 15-year loan does not merely cost more each month — it can reduce the house you are allowed to buy.

The third column is remarkably close to the second. Giving up $51,660 over sixteen years buys the permanent right to drop back to $2,528.27 in any month you want to, without asking anyone. Whether that option is worth $270 a month is the actual decision.

Shorter mortgages price lower because the lender's money is at risk for less time and the loan's duration is less sensitive to rate moves. The gap moves with market conditions — it is usually somewhere between a quarter and three quarters of a percentage point, and it is published weekly alongside other benchmark rates by sources such as the Federal Reserve's H.15 selected interest rates release (federalreserve.gov, read September 2026).

That discount is the strongest argument for the 15-year loan, and it is the one argument a disciplined prepayer cannot replicate. You can choose to pay like a 15-year borrower. You cannot choose to be charged like one. Everything else about the shorter term — the faster payoff, the smaller total interest, the equity curve — can be reproduced voluntarily on a 30-year note. The rate cannot.

So the question sharpens: is the rate discount worth surrendering the flexibility? On these numbers it is worth $51,660 over sixteen years, roughly $270 a month. If your income is stable and high relative to the payment, that is money for nothing and the 15-year is the better loan. If your income is variable, or the payment is a stretch, you are paying $270 a month to remove your own emergency lever, which is a poor trade at any discount.

No 15 year vs 30 year mortgage calculator can answer this part for you. Ignore the interest totals for a moment and answer one question: if my household income dropped by 25% for six months, could I still make the 15-year payment?

If yes, take the 15-year. The rate discount is free money and the forced discipline is a feature rather than a cost.

If no, take the 30-year and pay it like a 15-year. You will give up about $51,660 across the life of the loan and you will keep a $793.37 monthly release valve that requires no application, no approval, no fee and no explanation. Job losses, medical events and business downturns do not schedule themselves around amortization tables, and a mortgage payment you cannot suspend is the obligation that turns a bad year into a lost house.

If you are unsure, the answer is the 30-year. Uncertainty about your own income is itself information, and the flexible structure is the one that survives being wrong.

There is a behavioural counter-argument worth taking seriously: most people who plan to prepay do not, and the 15-year contract is the only version that guarantees the outcome. That is true, and it is the honest case for the shorter term. But the fix for weak discipline is an automatic transfer on payday, not a contract that also removes your ability to stop.

Your age and the loan's end date. A borrower who wants no mortgage at retirement has a hard deadline, and a 15-year loan is a straightforward way to meet it. This is one of the few situations where the forced schedule is precisely the point.

How long you will keep the loan. If you will sell or refinance within seven years, most of the 15-year advantage never materialises — the interest savings accrue over the back half of the term. Over a short horizon the two loans differ mainly in monthly cash-flow and in how much principal you have repaid at sale.

Whether you are leaving a retirement match on the table. An unclaimed employer match is an immediate guaranteed return that no mortgage rate competes with. Capture it before committing $793.37 a month to a shorter term. The SEC's investor education site has a plain-language primer on saving and investing basics (investor.gov, read September 2026).

Your mortgage rate relative to safe alternatives. At 6.5%, prepaying is an excellent guaranteed return and the 15-year case is strong. At 3%, the argument for tying up money in a cheap fixed-rate mortgage is far weaker, and the 30-year starts to look less like a compromise and more like the correct answer.

The tax deduction, which matters less than people think. Mortgage interest is deductible only if you itemise, and the higher standard deduction means most households no longer do. Do not let a deduction you are not claiming justify a term you did not want; IRS Publication 936 (irs.gov, read September 2026) sets out the actual rules.