Mortgage calculator

How to calculate a mortgage payment

1. Enter the home price and choose your down payment as a percentage or fixed amount.
2. Enter the annual interest rate and select a term in years.
3. Optionally add property tax percentage and yearly home insurance.
4. Review the monthly payment, total interest, and year-by-year amortization schedule.

Common uses

• Checking a lender's quote: enter the same home price, down payment, rate and term, then compare the monthly principal-and-interest figure before adding tax and insurance.
• Choosing a term: switch between 15, 20 and 30 years to see how a lower monthly payment trades against total interest.
• Planning the purchase budget: project how your down-payment savings grow, or price a car or personal loan that shares the same monthly budget.

The finance tools guide compares the five finance calculators and the formulas behind them.

Technical specification

• Algorithm or formula: Standard amortization formula M = P[r(1+r)^n] / [(1+r)^n - 1], where P is principal, r is monthly interest rate, and n is total number of monthly payments. PITI adds monthly property tax and insurance on top. This is the level-payment (annuity) formula for a fully amortizing loan; see Kellison, The Theory of Interest (3rd ed., McGraw-Hill/Irwin, 2009), on annuities and amortization schedules.
• Browser API or library: Pure JavaScript arithmetic; no external library. Uses Number primitives for all calculations.
• Input limits: Home price above 0. Rate of 0% or more; a result too large to calculate shows a note instead of figures. Term 1–50 years. Down payment of 0 or more and less than the home price.
• Output: Monthly principal-and-interest payment, monthly PITI, total interest paid over the loan, and a year-by-year amortization table showing the running balance, principal, and interest each year.
• Known limitations: Fixed-rate amortization only; ARM, balloon, and interest-only mortgages are not modeled. Tax and insurance are treated as constant over the loan term. Extra or irregular principal payments are not modeled; the schedule assumes the same payment every month.

Frequently asked questions

How is a monthly mortgage payment calculated?

Principal and interest follow the amortization formula M = P[r(1+r)^n] / [(1+r)^n - 1], where P is the loan amount, r is the monthly interest rate, and n is the number of monthly payments. Property tax and home insurance are added on top for the full PITI payment.

What does PITI stand for?

PITI is principal, interest, taxes, and insurance, the four components that typically make up a total monthly housing payment. The calculator adds optional tax and insurance to the standard principal-and-interest figure.

How does the loan term affect total interest?

Longer terms reduce the monthly payment but increase total interest, because principal is paid down more slowly. A 30-year mortgage at the same rate as a 15-year usually produces more than double the total interest.

Is my mortgage data sent to a server?

All calculations run locally in your browser as JavaScript. Our servers are not involved at any point.