This calculator works out your monthly repayment from the property price, deposit, term and interest rate you enter — choose between a standard repayment mortgage or an interest-only mortgage to see how the figures differ.
On a repayment mortgage, each monthly payment is split between interest on the amount you still owe and a portion that reduces the loan itself. Early in the term, more of each payment goes towards interest because the outstanding balance is higher; as the balance falls, a larger share goes towards capital. The calculator spreads payments evenly across the term so the total monthly amount stays the same throughout, even though the interest/capital split shifts each month.
With a repayment mortgage, your monthly payments cover both interest and capital, so the loan is fully paid off by the end of the term. With an interest-only mortgage, your monthly payments cover the interest only — the original loan amount remains outstanding throughout and must be repaid in full at the end of the term, usually from savings, an investment plan, or the sale of the property.
Three things have the biggest impact on your monthly repayment: the interest rate (even a small change can add hundreds of pounds a month on a large loan), the mortgage term (a longer term lowers the monthly amount but increases the total interest paid), and the size of your deposit (a larger deposit reduces the loan amount and can unlock lower interest rates by reducing your loan-to-value ratio).
Overpaying your mortgage means paying more than your required monthly amount, with the extra going directly towards reducing the capital you owe — this can significantly cut the total interest you pay and shorten your mortgage term.
Because interest is calculated on your outstanding balance, every extra pound you pay towards capital reduces the interest charged in every future month, not just the one you paid it in. Over a long mortgage term, even a modest monthly overpayment can save thousands of pounds in interest and take years off your mortgage. Switch on the overpayment toggle above and enter a monthly amount to see the effect on your own figures.
Most UK lenders allow you to overpay by up to 10% of your outstanding mortgage balance each year without charge. Overpaying beyond this limit can trigger an Early Repayment Charge (ERC), typically a percentage of the amount overpaid. If you're planning significant overpayments, check your mortgage offer or speak to your lender first to confirm your specific allowance.
Stamp Duty Land Tax (SDLT) is a one-off tax paid when you buy a property in England or Northern Ireland. It's not part of your mortgage loan or monthly repayment, but it's included here because it's a significant upfront cost that affects how much cash you need to complete a purchase.
Stamp duty is due to HMRC at completion and is normally paid from your own funds — alongside your deposit, legal fees, and other moving costs — rather than financed as part of your mortgage. Some buyers choose to increase their mortgage loan to help cover it, which would increase both the loan amount and the monthly repayment shown above. For a full breakdown of stamp duty thresholds, surcharges, and rates for Scotland and Wales, use the dedicated Stamp Duty Calculator.