Mortgage Calculator
Free mortgage calculator — work out your monthly payment, total cost over the life of the loan, and total interest paid. Just enter the loan amount, interest rate and term. Runs in your browser, no sign-up.
The monthly payment on a fixed-rate mortgage is fully determined by three numbers: the loan amount, the interest rate, and how long the loan runs. Type those in and the calculator returns your monthly principal-and-interest payment, the total amount you’ll pay over the life of the loan, and how much of that total is interest.
The formula
A fixed-rate mortgage is an amortizing loan — every monthly payment is the same, but the share that goes to interest vs. principal shifts over time. The monthly payment M is:
M = P × r(1 + r)^n ÷ ((1 + r)^n − 1)
where P is the loan amount, r is the monthly interest rate (the annual
rate divided by 12, expressed as a decimal — so 6.5% APR becomes
0.065 ÷ 12 ≈ 0.005417), and n is the total number of monthly payments
(years × 12).
What it doesn’t include
This is the principal and interest portion only. Your real housing payment will also include property taxes, homeowners insurance, HOA dues if any, and private mortgage insurance (PMI) if you put down less than 20%. Lenders bundle those into a single “PITI” payment and collect them through an escrow account. None of those depend on the amortization math — they’re just added on top.
Term length is a lever
The same loan over 15 vs. 30 years has a very different total cost. A 15-year loan pays much less interest because the principal is being paid down faster and there’s simply less time for interest to accumulate. Use the calculator to compare side by side: shorten the term and watch total interest fall, even though the monthly payment rises.
Worked examples
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$350,000 home loan at 6.5% over 30 years
Monthly payment: $2,212.24 — total $796,405.71 over 30 years (interest: $446,405.71).
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$200,000 loan at 7% over 15 years — the same loan paid off in half the time
Monthly payment: $1,797.66 — total $323,578.18 over 15 years (interest: $123,578.18).
Frequently asked questions
How is the monthly mortgage payment calculated?
The standard amortizing-loan formula. If P is the loan amount, r is the monthly interest rate (annual rate ÷ 12 ÷ 100) and n is the total number of months (years × 12), the payment is M = P × r(1 + r)^n ÷ ((1 + r)^n − 1). Each month a constant amount comes out: at the start most of it is interest, by the end most of it is principal.
Does this include property tax, homeowners insurance or PMI?
No — this is just the principal and interest (P&I) part of the payment, the part that the bank's amortization schedule pins down. Your actual escrow payment will be higher once you add property taxes, homeowners insurance, HOA dues, and (if you put down less than 20%) private mortgage insurance. Estimate those separately and add them on.
Why does total interest drop so much when I shorten the term?
Because every extra month you carry the loan is another month the bank is charging interest on the remaining balance. A 15-year loan pays roughly a third of the interest of a 30-year loan at the same rate, even though the monthly payment is only about 50% higher — you finish much sooner, so interest has far less time to compound.
How much does the interest rate actually matter?
Enormously. On a $350,000 30-year mortgage, going from 6% to 7% adds roughly $230 to the monthly payment and about $80,000 to the total interest over the life of the loan. Even a 0.25% difference is worth shopping for.
What if I make extra payments?
This calculator assumes a fixed monthly payment that exactly pays off the loan over the chosen term. Any extra principal you pay early in the loan shortens the term and saves a disproportionate amount of interest, because it knocks down the balance the bank is charging interest on for the rest of the loan.