The 15-year mortgage is always cheaper in total — that part is not in dispute. What matters is the monthly difference, and whether that money does more for you locked into home equity or kept liquid. This calculator puts both loans side by side, including equity built at the milestone you choose.
Lowest lifetime cost
Lowest monthly payment — most flexibility
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The 15-year always costs less in total and builds equity far faster; the 30-year always has the lower required payment. The real question is whether the monthly difference is better spent forcing equity into the house or kept as financial flexibility.
Typically 0.50 to 0.75 percentage points below the 30-year, because the lender's risk exposure is shorter. The spread moves with the market, so ask for both on the same loan estimate rather than comparing quotes from different days.
Usually more than half the lifetime interest. On a $400,000 loan the difference commonly exceeds $200,000 — a function of both the lower rate and the far shorter period over which interest accrues.
Close to it. Taking a 30-year and voluntarily paying it on a 15-year schedule captures most of the interest savings while keeping the lower required payment as your floor if income drops. You give up the 15-year's lower rate to buy that flexibility.
They earn substantially more interest over the longer term, and the lower payment qualifies more borrowers at a given income. That is not a reason to avoid the 30-year — but it is a reason to run the comparison yourself.
Sources: Freddie Mac Primary Mortgage Market Survey — 15- and 30-year averages; CFPB — choosing a loan term; Standard amortization (annuity) formula.
Estimates for educational purposes only — not a loan offer, financial advice, or a commitment to lend. Actual rates, payments, and terms vary by lender and creditworthiness.