Guide · Mortgage

15-year vs 30-year mortgage math

Educational guide · Updated · About 6 min read

Term length is a trade-off between monthly principal-and-interest and total interest paid—under a fixed rate model.

Sample: $350,000.00 · 20% down · 6% rate

  • 15-year: $2,362.80 P&I/mo · $145,303.84 interest
  • 30-year: $1,678.74 P&I/mo · $324,346.93 interest

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Frequently asked questions

Does a 15-year mortgage always cost less interest?

Under the same fixed rate and loan amount in Nestfigure’s model, a 15-year term usually has higher monthly P&I and lower total interest than a 30-year term. Real rates and costs can differ by product.

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Compare terms in the free calculator

Same price and rate, different lengths.

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Sources linked above include U.S. government materials (for example CFPB, FDIC, NCUA, BLS, IRS) where noted. Sample math uses only labeled Nestfigure assumptions—not bank quotes, job offers, or personalized advice. Last reviewed: August 9, 2026.

YMYL notice: This site is for education only. It is not financial, tax, or investment advice. Nestfigure is not a bank, credit union, broker, investment adviser, or fiduciary. Product terms, rates, and penalties vary—always read your institution’s disclosures before acting. Calculator results are mathematical estimates, not bank quotes.