RunToolRunMortgage Calculator
Calculate mortgage payments.
How to Calculate a Mortgage Payment
Enter the loan details
Loan amount, annual interest rate and term in years.
The payment is computed instantly
The standard amortization formula runs in your browser.
Review monthly cost and totals
See the monthly payment, total interest and total amount repaid.
Where the monthly payment comes from
A repayment mortgage is an annuity: a fixed monthly amount chosen so that, at a given interest rate, the balance reaches exactly zero at the end of the term. Each payment covers the interest accrued that month, and whatever remains reduces the principal.
Because interest is charged on the outstanding balance, and the balance falls slowly at first, the split between interest and principal shifts over the life of the loan. The payment stays the same; what it buys changes completely.
Why early payments barely touch the debt
In the first years of a long mortgage, the overwhelming majority of each payment is interest. On a typical 25- or 30-year loan, it can take a third of the term before principal and interest are even in each payment.
This is the single most useful thing an amortisation schedule shows, and it surprises almost everyone who looks at one for the first time. It is also why total interest paid over a full term can approach or exceed the amount borrowed.
The term is the biggest lever
Extending a mortgage from 25 to 30 years reduces the monthly payment noticeably and increases total interest substantially, because the balance stays high for longer. Shortening it does the reverse: a higher monthly cost and a much lower total.
Overpayments work through the same mechanism. Because an extra payment reduces principal directly, it removes all the future interest that principal would have generated — which is why a modest regular overpayment early in the term can shorten a mortgage by years. Check whether your lender permits it without penalty before relying on it.
What the monthly figure leaves out
The calculated payment covers principal and interest only. The actual cost of owning a home adds property tax, buildings insurance, mortgage insurance where the deposit is small, service charges or ground rent on leasehold property, and maintenance — which is easy to forget and never zero.
Budgeting from the mortgage payment alone is the standard way to end up stretched. The advertised rate is also not the whole cost: an APR that includes fees is a better comparison between offers than the headline rate.
Fixed, variable, and the limits of a model
A fixed rate makes the calculation exact for the fixed period only. After it ends, the rate changes and so does the payment — often substantially. A variable rate means the schedule is an illustration from the first month onwards, not a prediction.
This calculator is arithmetic, not advice, and it cannot account for your circumstances, your lender's specific terms, or where rates go next. Everything runs in your browser, so income, deposit and loan figures you enter are not transmitted anywhere — unlike most mortgage calculators on lender and broker sites, which exist partly to collect exactly those numbers.