How mortgage payments are calculated
Understand principal, interest, term, taxes and insurance before using a mortgage estimate.
Last reviewed: 2026-07-29A standard fixed-rate payment is based on the borrowed principal, monthly interest rate and number of monthly payments. Property tax and insurance may then be added to estimate the full monthly outlay.
Principal and interest
Principal is the home price minus the down payment. The interest rate is converted to a monthly rate, and the term determines the number of payments.
With a fixed-rate amortizing loan, the principal-and-interest payment stays level, but early payments contain more interest and later payments contain more principal.
What the estimate may omit
A real payment can also include property taxes, homeowners insurance, mortgage insurance, association fees or other charges. Rates, rules and closing costs vary by lender and location.
A calculator is useful for comparing scenarios, not for approving a loan or predicting a lender’s final offer.
How to test scenarios
Compare a larger down payment, a shorter term and several plausible rates. Keep taxes and insurance separate so you can see what comes from the loan and what comes from ongoing ownership costs.