Mortgage repayment calculator: understand the numbers
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Estimate monthly capital-and-interest repayments and compare the effect of the loan amount, term and an illustrative interest rate.
Enter the amount you would borrow
Use the loan amount rather than the entire property price. Enter an annual nominal interest rate and the term in years. This model assumes equal monthly repayments and an unchanged rate for the whole term. It is a mathematical illustration, not a lender quotation or approval.
Change one input at a time. Keeping amount and term fixed shows the effect of the assumed rate. Keeping amount and rate fixed shows the trade-off between shorter and longer terms. Actual products may change rate, include fees or have conditions absent from this model.
How the calculation works
For a positive monthly rate r and n monthly payments, the payment is P × r ÷ (1 − (1 + r) raised to −n). P is the starting loan; r is the annual percentage divided by 100 and then 12. At a zero rate, the payment is P divided by n.
Total interest is the unrounded monthly payment multiplied by the payment count, minus the starting loan. The display rounds to whole euro. A lender’s timing, rounding and interest conventions can differ.
A worked comparison
For a €300,000 loan at a constant illustrative 4% over 30 years, the model gives about €1,432 a month. Over 25 years at the same assumed rate, it gives about €1,584. These invented assumptions explain the arithmetic; they are not claims about available rates.
A longer term can reduce the monthly figure while increasing total interest. Compare both. For background on amortisation, see the Consumer Financial Protection Bureau explanation. That source discusses US mortgages; this tool applies only the general mathematical model.
What is excluded
Fees, insurance, taxes, rate changes, missed payments, overpayments and product-specific conditions are excluded. A fixed initial period does not mean the same rate applies for the entire term. Ask the lender how payments change afterwards.
Keep a separate budget for housing costs beyond repayments. Compare official lender disclosures using consistent assumptions. Nothing entered here is sent to a lender or used to assess creditworthiness: the arithmetic runs inside your browser.