Mortgage payment calculator

Work out the principal-and-interest payment on a fixed-rate mortgage, and see how much of the total goes to interest over the term.

How this calculator works

This is the principal-and-interest (P&I) part of a mortgage payment — the amount that repays the loan itself. Your real monthly bill usually also includes property tax, homeowners insurance and possibly mortgage insurance, which lenders collect in escrow and which are not part of this calculation.

The maths is identical to any amortising loan, but the numbers matter more because the term is long. At 6% over 30 years, more than half of every early payment is interest. A shorter term or a lower rate shifts that balance dramatically: a 15-year loan at the same rate carries a payment about 35% higher but cuts total interest by roughly 60%.

The formula

For mortgage amount P, monthly rate r = APR ÷ 12 ÷ 100 and n = term in months:

Multiply M by n for total payments; subtract P for total interest. The common shortcut “multiply the loan by 6% for a 30-year loan” is not accurate — the true total interest at 6% over 30 years is about 116% of the amount borrowed.

Worked example

The default 250,000 mortgage at 6% for 30 years has a principal-and-interest payment of $1,498.88. Over the full term you would repay $539,595.47, so $289,595.47 — more than the amount originally borrowed — goes to interest.

Common mistakes

• Forgetting escrow. Property tax and insurance can add 20–40% to the P&I figure. Budget with a full PITI estimate, not just this number.
• Comparing rates without points. A lower rate bought with discount points is not free; divide the point cost by the monthly saving to see the break-even months.
• Assuming the payment never changes. This figure is for a fixed-rate loan. Adjustable-rate mortgages reset on a schedule and can move sharply.