Two amortizing loans, same principal
A 15-year fixed mortgage is paid in 180 months; a 30-year loan is paid in 360. The 15-year quote is often a lower rate. This page amortizes the same principal at the two rates you enter and reports the extra monthly payment and the interest difference. The mortgage page prices one loan from a home price. Refinance replaces a remaining term. Biweekly is a payment-frequency estimate on one schedule.
30-year payment = amortizing payment over 360 months
Total interest = payment × months − principal
Interest saved = 30-year total interest − 15-year total interest
At 0%, payment is principal ÷ months
Example
On a $300,000 loan, 6.25% for 15 years and 7% for 30 years, the 15-year payment is about $2,572.27 and the 30-year payment is about $1,995.91. The 15-year loan costs about $255,518 less in interest and about $576 more each month.
What this comparison leaves out
Taxes, insurance, HOA, PMI, and points stay out of both payments. Qualifying DTI uses the higher 15-year payment. Opportunity cost of the extra monthly amount is not modeled. Enter the actual quoted rate for each term. If the result for interest saved is negative, the 15-year rate you entered makes its total interest higher in this comparison.