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Mortgage Calculator

Estimate the monthly principal and interest on a home loan. Enter the price, your down payment, the term and the rate — the standard amortization formula does the rest, in your browser.

Standard amortization formulaHandles 0% loansNothing leaves your browser

Estimate your monthly payment

Change any field and the payment, total interest and total cost recalculate immediately.

Principal & interest

$2,022.62/ month

Home price$400,000.00
Down payment$80,000.00
Loan amount$320,000.00
Number of payments360
Total interest$408,142.36
Total paid over the term$728,142.36

These figures are estimates for planning only. The payment shown covers principal and interest only, and excludes property tax, homeowners insurance, PMI, HOA dues, closing costs and lender fees — all of which vary by property and location. Lenders also differ in how they round and accrue interest, so an actual quote will differ from this number.

Using the mortgage calculator

  1. Enter the price and deposit

    Type the home price, then give the down payment either as a dollar amount or as a percentage — editing one field updates the other automatically.

  2. Set the term and rate

    Choose how many years the loan runs for and enter the annual interest rate your lender has quoted. A rate of 0 is accepted and handled correctly.

  3. Read the breakdown

    You get the monthly principal-and-interest figure, the amount actually borrowed, the number of payments, total interest, and the total paid by the end of the term.

What the calculator covers

And, just as importantly, what it does not.

  • The standard formula

    Monthly payment is M = P × r ÷ (1 − (1 + r)⁻ⁿ), where r is the annual rate divided by twelve and n is the number of monthly payments — the level-payment maths lenders amortize with.

  • Zero-interest handled

    At a 0% rate that formula divides by zero. This calculator detects the case and splits the principal evenly across the term instead, so a 120,000 loan over 10 years returns exactly 1,000 a month.

  • Deposit in dollars or percent

    The two down payment fields stay in sync, so you can think in whichever one your savings are framed in without doing the arithmetic yourself.

  • Terms from 10 to 40 years

    Switch the term and watch both numbers move — a longer term lowers the monthly payment and raises the total interest, usually by more than people expect.

  • Lifetime cost, not just the payment

    The summary shows total interest and total paid across the whole loan, which is where term length and rate differences really show up.

  • Runs in your browser

    Price, deposit and rate are never sent anywhere. There is no account, no logging, and no network request behind the result.

How the monthly payment is worked out

A repayment mortgage is a level-payment loan: you pay the same amount every month, and each payment covers the interest accrued that month with the remainder reducing the balance. Early on almost all of it is interest; by the end almost all of it is principal.

The formula that produces a payment which lands the balance exactly on zero at the final instalment is M = P × r ÷ (1 − (1 + r)⁻ⁿ). P is the amount borrowed after your deposit, r is the monthly interest rate, and n is the total count of payments. When r is zero there is no interest to cover, and the payment is simply the principal divided by the number of months.

What this number leaves out

The figure above is principal and interest. A real monthly housing cost usually also includes property tax, homeowners insurance, private mortgage insurance if the deposit is under the lender threshold, and HOA or service charges. Together those can add a substantial amount that this calculator does not attempt to guess, because they depend entirely on the specific property.

One-off costs sit outside it too: origination and appraisal fees, title work, legal costs and moving expenses. Some of those can be rolled into the loan, which raises the principal and therefore the payment. Treat the output here as the loan component of the budget, not the whole of it.

Why the term changes the total so much

Extending a mortgage lowers each payment because the principal is spread over more instalments, but interest keeps accruing on the outstanding balance the entire time. A longer term therefore means a smaller payment and a larger total cost, and the gap widens quickly as rates rise.

Run the same price and rate at a few different terms to see the trade-off in your own numbers. The comparison is more informative than any rule of thumb, because how much the total moves depends heavily on the rate you are actually being offered.

Mortgage Calculator FAQ

With the level-payment amortization formula: M = P × r ÷ (1 − (1 + r) to the power of −n). P is the amount borrowed, r is the annual interest rate divided by twelve, and n is the number of monthly payments. That produces a constant payment which clears the balance exactly on the final instalment.

Property tax, homeowners insurance, PMI, HOA or service charges, closing costs and lender fees are all excluded. The result is principal and interest only. Your actual monthly outgoing on the property will be higher, and by how much depends on where the property is.

The calculator switches to dividing the principal evenly across the number of payments, because the standard formula is undefined at a zero rate. A 120,000 loan over 10 years returns exactly 1,000.00 a month, with zero total interest.

On the purchase price. Twenty percent down on a 400,000 home is 80,000, leaving 320,000 to borrow. That is also the convention lenders use when they set thresholds for mortgage insurance, so the percentage here lines up with the one they quote.

It reduces the amount borrowed, and the payment falls in proportion: at the same rate and term, borrowing 10% less gives a payment 10% lower. A larger deposit can also clear the lender’s threshold for mortgage insurance, a saving this calculator does not model.

Because interest accrues on the outstanding balance for every month the loan runs. Stretching the term reduces each payment but leaves a larger balance outstanding for longer, so total interest rises. Try the same figures at two different terms and compare the total interest line.

Generally yes. Extra money applied to principal lowers the balance that interest is charged on, so the loan ends sooner and costs less in total. This mortgage calculator assumes the same payment every month and does not model overpayments, and some loans carry prepayment penalties, so check your terms with the lender.

Treat them as a planning estimate rather than a quote. Lenders differ in how they round, when they accrue interest and what fees they roll into the loan, and the escrow items above are not modelled at all. Get a written illustration from a lender before committing.

Planning the home, not just the loan

Think through the layout of the place you are buying — describe the rooms and generate a labelled floor plan image before you commit.

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