A mortgage payment is mostly arithmetic, but it is arithmetic with a lot of moving parts. This calculator combines the loan math with the costs that usually ride along with it — property tax, homeowners insurance, private mortgage insurance and HOA dues — so the number you see is close to what actually leaves your account each month.
How to use the mortgage calculator
- Enter the home price and your down payment, either as a percentage or a dollar amount.
- Enter the interest rate you have been quoted and pick a loan term.
- Optionally add yearly property tax and insurance, a PMI rate, monthly HOA dues and any extra principal you plan to pay.
- Read the monthly payment on the tape, then scroll for the balance chart and the yearly and monthly amortization schedules.
The mortgage payment formula
For a fixed-rate loan the principal-and-interest payment is the same every month:
- P is the amount borrowed (price minus down payment).
- r is the monthly interest rate: the annual rate ÷ 12. A 6.5% rate gives r = 0.0054167.
- n is the number of payments: years × 12.
Each month, interest is charged on the remaining balance (balance × r) and the rest of the payment reduces the principal. Early payments are mostly interest; by the final years they are mostly principal. The amortization table shows that shift month by month.
Worked example
A $400,000 home with 20% down leaves a $320,000 loan. At 6.5% for 30 years:
- r = 0.065 ÷ 12 = 0.00541667 and n = 360
- (1 + r)360 ≈ 6.9917
- M = 320,000 × 0.00541667 × 6.9917 ÷ 5.9917 ≈ $2,022.62 per month
Adding $400 a month of property tax and $125 of insurance brings the full payment to about $2,547.62. Over 30 years the borrower pays roughly $408,000 in interest — more than the loan itself — which is why a lower rate or a shorter term matters so much.
What changes your payment the most
| Change | Effect on a $320,000, 30-year loan |
|---|---|
| Rate drops from 6.5% to 6.0% | Payment falls about $104 a month |
| Term shortens from 30 to 15 years | Payment rises about $765, but total interest falls by roughly $226,000 |
| Down payment rises from 10% to 20% | Smaller loan and no PMI |
| $200 extra principal per month | Loan paid off about 7 years early |
Costs this calculator does not include
Closing costs, origination fees, discount points and moving expenses are paid up front rather than monthly, so they are not part of the payment. Adjustable-rate mortgages change after their fixed period; this calculator assumes the rate stays the same for the full term. Lenders also look at your debt-to-income ratio before approving a payment — see the house affordability calculator for that side of the question.
Results are estimates for planning. Your lender's Loan Estimate is the authoritative figure for any specific loan.
Frequently asked questions
How is a monthly mortgage payment calculated?
The principal-and-interest part uses the standard annuity formula M = P·r(1+r)^n ÷ ((1+r)^n − 1), where P is the loan amount, r is the annual rate divided by 12 and n is the number of monthly payments. Property tax, insurance, PMI and HOA dues are then added on top.
What is PITI?
PITI stands for principal, interest, taxes and insurance — the four parts of a typical monthly house payment when taxes and insurance are collected through an escrow account.
When does PMI go away?
On conventional loans, private mortgage insurance is required when you put down less than 20%. US lenders must cancel it automatically once your balance is scheduled to reach 78% of the original home value, and you can usually ask to remove it at 80%.
How much do extra payments save?
Every extra dollar goes straight to principal, which reduces the interest charged in every month that follows. Enter an amount in the extra-principal field to see the interest saved and how many months sooner the loan is paid off.
Should I choose a 15-year or 30-year mortgage?
A 15-year loan has a higher monthly payment but a lower rate and far less total interest. A 30-year loan keeps the payment lower and leaves more monthly flexibility. Compare both terms in the calculator to see the trade-off for your numbers.