A $620,000 home with 20% down at 6.5% over 30 years has a principal-and-interest payment of $3,135.06 a month. That monthly payment on a fixed-rate mortgage covers interest on the outstanding balance plus enough principal to retire the loan exactly at the end of the term, and it is computed with the standard amortization formula from the amount financed (home price minus down payment), the monthly interest rate, and the number of payments.
Your 6.5% is right around the average 30-year fixed mortgage rate of 6.43%. Freddie Mac PMMS, as of July 2026.
Suppose you put the default values into Mortgage Calculator:
Plug those into the formula M = P · [r(1+r)^n] / [(1+r)^n − 1] and the result is:
In a real mortgage, the bank would also add escrow for taxes and insurance, possibly PMI if your down payment is under 20%, and an origination fee — none of which appear in this calculator. The payment shown is principal-and-interest only.
| Interest rate | Monthly payment | Total paid |
|---|---|---|
| 5% | $2,662.64 | $462,549 |
| 5.5% | $2,816.23 | $517,844 |
| 6% | $2,973.77 | $574,557 |
| 6.5% | $3,135.06 | $632,621 |
| 7% | $3,299.90 | $691,964 |
| 7.5% | $3,468.10 | $752,517 |
The mortgage payment formula is the standard amortization equation used by every U.S. lender. We compute interest monthly (rate / 12), which matches how mortgage servicers actually charge interest. Extra payments are applied directly to principal in the following month, which is the most common loan structure but not universal — check your loan terms.
References: CFPB methodology; Federal Reserve.
Last reviewed July 2, 2026 · Editorial policy