Result
How to use this calculator
Enter your loan amount and the rate you were quoted for each term. The calculator shows the monthly payment, total interest, and payment difference side by side — no need to run two tools and compare by hand.
The formula
Both sides use the standard amortization formula M = L × r(1+r)^n ÷ ((1+r)^n − 1). The 15-year side uses the 15-year rate and 180 payments; the 30-year side uses its rate and 360 payments.
Example: $400,000
At 5.5% for 15 years vs 6.5% for 30 years: the 15-year payment is about $3,268.33 vs $2,528.27 — but total interest is roughly $188,000 vs $510,000. The shorter term costs $740 more per month and saves about $322,000 in interest.
FAQ
How much cheaper is a 15-year mortgage overall?
On $400,000 at 5.5% vs 6.5%, total interest is roughly $188,000 vs $510,000 — the 15-year saves over $320,000 across the loan, though its payment is about 29% higher.
Why is the 15-year rate lower?
Lenders take less rate risk on shorter loans and 15-year borrowers default less, so pricing is tighter. The gap is often 0.5-0.75 percentage points.
Can I get 30-year flexibility with 15-year speed?
Yes — many borrowers take the 30-year loan and voluntarily pay the 15-year amount each month. You keep the lower required payment as a safety valve.
Which is better for investing the difference?
If your expected investment return beats your mortgage rate after tax, the 30-year with invested savings can win mathematically — but it carries behavioral and market risk.