Mortgage Calculator — monthly payment, in your browser

Buying a home is a big decision, and a clear payment estimate makes it easier to plan. Enter the home price, your down payment, the loan term and the interest rate, and this calculator instantly shows your monthly principal and interest, plus optional property tax and insurance.

Everything is computed locally with the standard amortization formula, so your numbers never leave your device — no account, no uploads and no tracking. Adjust any field and the results recalculate the moment you type.

How it works

Your monthly principal-and-interest figure comes from the standard amortization formula, M = P·r·(1+r)ⁿ / ((1+r)ⁿ − 1). The loan amount P is the home price minus your down payment, r is the annual interest rate divided by 12, and n is the loan term in years multiplied by 12. If you add annual property tax and home insurance, each is divided by 12 and added on top to give the full monthly cost.

The key thing the formula reveals is how a single payment splits between interest and principal. Interest is charged on the balance you still owe, so early in the loan — when the balance is highest — most of each payment goes to interest and only a sliver pays down the principal. As the balance shrinks, that ratio flips and later payments are mostly principal. This is amortization, and it is why paying a little extra in the early years has an outsized effect.

Every calculation runs in JavaScript inside your own browser. There is no server round-trip, no account and no upload — the home price, your down payment and the rate never leave your device, and they are gone the moment you close the tab.

When to use it

Reach for this before you start house-hunting in earnest, so you shop in a price range whose monthly payment actually fits your budget rather than working backwards from a listing. It is just as useful for comparing scenarios side by side: a shorter term versus a longer one, a larger down payment versus a smaller one, or two lenders quoting different rates.

Looking at the total interest, not just the monthly payment, is where the comparison pays off. A longer term lowers the monthly figure but usually raises the lifetime interest considerably, while a bigger down payment cuts both. Because nothing is stored or transmitted, you can run dozens of what-if combinations privately, including with sensitive numbers you would not want typed into a lead-generation form.

Tips

Treat the output as a planning estimate, not a quote. It covers principal, interest and the optional tax and insurance you enter, but not PMI, HOA dues, closing costs or escrow adjustments, so your real payment will typically run a bit higher. Enter property tax and insurance whenever you can — for many buyers they are a meaningful share of the monthly total and leaving them out makes a home look more affordable than it is.

When you compare offers, keep the loan amount and term fixed and change only the rate to see its true impact, then do the reverse to isolate the term. Finally, confirm the figures with your lender before committing: the formula is exact, but the inputs (your actual rate, taxes and fees) are what determine the payment you will really make.

How to use Mortgage Calculator

1. Enter the home price you are considering.
2. Set your down payment as a dollar amount or a percentage.
3. Choose the loan term in years and enter the annual interest rate.
4. Optionally add annual property tax and home insurance.
5. Read your estimated monthly payment, total interest and total cost — all updated live.

Frequently asked questions

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