DigiKitMortgage Calculator
Enter the home price, down payment, interest rate and loan term to see your estimated monthly payment and the total interest over the loan.
How a mortgage payment is calculated
A standard fixed-rate mortgage is repaid in equal monthly instalments. The calculator uses the usual amortization formula: M = P × r ÷ (1 − (1 + r)−n), where P is the loan amount (home price minus down payment), r is the monthly interest rate (annual rate ÷ 12 ÷ 100) and n is the number of monthly payments (years × 12). If the rate is 0%, the payment is simply P ÷ n.
Property tax and home insurance are added on top as monthly amounts: the tax is the home price × the annual tax rate ÷ 12, and insurance is the yearly figure ÷ 12. Both fields are optional, so leave them empty to see the loan payment alone.
Worked example
Take a home priced at 400,000 with 80,000 down (20%) on a 30-year loan at 6.5%. The loan amount is 320,000. The monthly principal and interest payment is 2,022.62, and over 360 payments you pay 728,142.36 in total, of which 408,142.36 is interest.
Now add a property tax rate of 1.1% and insurance of 1,800 a year (these are example figures, not typical values for your area). Tax adds 366.67 a month and insurance 150, so the total monthly payment comes to 2,539.28.
How the term, rate and down payment change the result
| Change (home price 400,000) | Loan | Monthly principal and interest | Total interest |
|---|---|---|---|
| Base case: 20% down, 6.5%, 30 years | 320,000 | 2,022.62 | 408,142.36 |
| Same, but 15 years | 320,000 | 2,787.54 | 181,757.84 |
| Same as base, but 5.5% rate | 320,000 | 1,816.92 | 334,092.93 |
| Same as base, but 10% down (40,000) | 360,000 | 2,275.44 | — |
A shorter term raises the monthly payment but cuts the total interest sharply, because the balance falls faster. A lower rate or a larger down payment reduces both the payment and the interest.
How to use the calculator
- Type the home price and the amount you plan to put down.
- Enter the annual interest rate quoted by your lender and the loan term in years.
- Optionally add the yearly property tax rate and the yearly insurance cost.
- Press Run to see the loan amount, the monthly payment and the total interest.
Things to keep in mind
- This is an estimate. It does not include mortgage insurance, HOA fees, closing costs or lender fees, and your actual payment can differ.
- Lenders often require mortgage insurance when the down payment is below 20% of the price; ask your lender how it applies to you.
- The calculator assumes a fixed rate for the whole term. An adjustable-rate loan changes over time and cannot be modelled with one rate.
- Property tax rates and insurance costs vary widely by location and home. Use figures from your local tax office or insurance quote rather than guessing.
- The result is not financial advice; compare offers from several lenders before you decide.
Frequently asked questions
What is included in the monthly payment?
The principal and interest payment is always included. Property tax and home insurance are included only if you fill in those optional fields. Mortgage insurance, HOA fees and utilities are not included.
Does the calculator work in any currency?
Yes. It does only arithmetic, so the numbers can be in dollars, pounds, euros or any other currency, as long as you use the same currency for the price, down payment and insurance.
Why is so much of the early payment interest?
Interest is charged on the remaining balance. At the start the balance is at its highest, so most of each payment goes to interest. As the balance falls, a larger share goes to principal.
What if the interest rate is 0%?
The calculator divides the loan amount by the number of payments, so there is no interest and the total interest shows 0.
Is my data stored?
No. The calculation runs in your browser and nothing you enter is sent to a server.