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15-Year vs 30-Year Mortgage: The Real Cost of Flexibility
A 30-year loan has a lower payment but far more total interest. See the exact numbers on a $350,000 loan and how to decide which fits your budget.
Written by James — Founder & Builder, BoringToolsKit · Published 2026 · Planning information, not professional advice.
The payment gap
On $350,000 at 6.5% for 30 years, principal and interest run about $2,212 per month. At 6.0% for 15 years, about $2,954 — roughly $742 more per month. That gap is the price of flexibility.
The interest gap
The 30-year borrower pays about $447,000 in interest over the life of the loan; the 15-year borrower about $182,000. The 15-year loan is dramatically cheaper, but it costs 33% more cash flow every month for 15 years.
Rates favor the shorter loan
Lenders typically price 15-year loans 0.5-0.75 points below 30-year rates because their risk window is shorter. That rate cut amplifies the interest savings beyond the term effect alone.
The hybrid strategy
Take the 30-year loan and voluntarily pay the 15-year payment. You keep the right to drop back to the lower payment during a rough month, and prepay aggressively otherwise. Check for prepayment penalties, and mark extra payments 'applied to principal'.
How to decide
Model both in the mortgage calculator with your real rate quotes. If the 15-year payment fits comfortably under 28% of gross income, the interest savings are compelling. If it strains the budget, the 30-year with disciplined extra principal captures most of the benefit with none of the risk.
Frequently asked questions
How much more interest does a 30-year loan cost?
On a $350,000 loan at 6.5% for 30 years, total interest is about $447,000. The same loan at 6.0% for 15 years costs about $182,000 — even with a slightly lower 15-year rate, the difference is enormous.
Can I get 30-year flexibility with 15-year economics?
Often yes: take the 30-year loan and pay extra principal each month. The tradeoff is discipline — the extra payment is optional, and many borrowers skip it.