Mortgage Interest Calculator: Total Interest by Term
See how much interest a fixed-rate mortgage costs over its full term and how a 15-year loan compares with a 30-year loan on the same balance.
Worked example
- Home price
- $400,000.00
- Down payment
- $80,000.00 (20%)
- Loan amount (P)
- $320,000.00
- Annual interest rate
- 6.5%
Same loan, different terms
| Loan term (years) | Monthly principal & interest (M) | Total interest (I) | Total principal & interest paid |
|---|---|---|---|
| 30 | $2,022.62 | $408,143.20 | $728,143.20 |
| 15 | $2,787.54 | $181,757.20 | $501,757.20 |
Formula
Total interest is everything you pay beyond the amount borrowed: the monthly principal and interest payment multiplied by the number of payments, minus the loan amount.
A shorter term raises the monthly payment but cuts total interest sharply, because the balance is repaid faster and accrues interest for fewer months. The comparison below uses the same loan amount and rate.
I = M × n − P
n = 360: I = 2,022.62 × 360 − 320,000 = 408,143.20
n = 180: I = 2,787.54 × 180 − 320,000 = 181,757.20
Estimates are informational only. They do not include closing costs, maintenance, utilities, or lender-specific fees. This is not financial, tax, or legal advice.
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