Content and calculation method reviewed: 10 October 2026
How does a mortgage calculator work?
A mortgage calculator estimates the regular payment needed to repay a home loan over a chosen period. It combines the mortgage amount, interest rate and repayment term using an amortization formula.
With an amortized mortgage, the payment can remain the same each month while the way that payment is divided changes. Early in the mortgage, a larger portion normally goes toward interest because the outstanding balance is still high. As the balance falls, more of each payment goes toward reducing the principal.
Mortgage payment formula
In this formula, P is the amount borrowed, r is the monthly interest rate and n is the total number of monthly payments.
CalcNator converts the annual percentage rate entered above into a monthly rate by dividing it by 12 and by 100. The mortgage term in years is converted into months.
Worked mortgage example
Suppose the mortgage amount is 250,000, the annual interest rate is 10%, and the term is 5 years.
Using the standard amortization formula, the estimated monthly principal-and-interest payment is approximately 5,311.76.
Over 60 monthly payments, the estimated total repayment is about 318,705.67, including roughly 68,705.67 in interest.
The figures use the same currency as the mortgage amount you enter. They do not include additional property or lender costs.
What affects your monthly mortgage payment?
Three inputs have the biggest effect on the basic principal-and-interest payment:
- Mortgage amount: borrowing more normally increases both the monthly payment and the total interest paid.
- Interest rate: a higher rate increases the cost of borrowing because more interest is charged on the outstanding balance.
- Mortgage term: spreading repayment across more years can reduce the monthly payment, but it can also increase total interest because the balance remains outstanding for longer.
How to compare mortgage scenarios
Instead of relying on a single calculation, change one input at a time. This makes it easier to understand which part of the mortgage has the biggest effect on affordability.
- Reduce the mortgage amount to see the effect of making a larger deposit.
- Compare shorter and longer terms to see the trade-off between monthly affordability and lifetime interest.
- Try a higher interest rate to see how your payment could change if borrowing costs are higher than expected.
- Compare the result with the actual quotation supplied by a lender before making a financial decision.
What does this mortgage calculator include?
This calculator is designed around the core principal-and-interest calculation for a fixed-rate, fully amortizing mortgage with monthly payments.
The result includes:
- estimated monthly principal-and-interest payment;
- estimated total repayment over the selected term;
- estimated total interest;
- an amortization schedule showing how the balance changes after each payment.
What does the estimate leave out?
Your real housing cost may be higher than the number shown by the calculator. Depending on your lender and location, other costs may include property taxes, homeowners insurance, mortgage insurance, levies, account fees, transfer or closing costs, legal charges and other lender-specific expenses.
Variable or adjustable-rate mortgages also require extra assumptions because future interest rates are unknown. This calculator can be used to compare individual rate scenarios, but it cannot predict future rate changes.
About this calculation
CalcNator uses the standard amortization equation shown on this page. Inputs are processed in your browser and the results are estimates rather than lender quotations.
For information about rounding, calculator assumptions and how results should be interpreted, see Methodology & Accuracy .
Mortgage calculator vs loan calculator
Both mortgage and general loan calculators can use similar amortization mathematics. The difference is mainly the context. A mortgage is secured against property and may involve housing-specific costs that are not normally part of a basic personal-loan calculation.
For borrowing that is not connected to property, use the CalcNator Loan Calculator .
Learn more about mortgage calculations
For a deeper explanation of amortization, mortgage payment calculations and costs that a basic calculator may not include, read the Mortgage Calculator Guide .