Mortgage repayment calculator (UK)

This tool assumes you already know (or have chosen) a loan amount, property price, or deposit, and just want the payment and full amortization schedule — including repayment vs. interest-only and rate-change scenarios the affordability tool doesn't model. The house affordability calculator works from the other direction — it estimates how much you could borrow in the first place from your salary, existing debts, and deposit, including stamp duty and a lender affordability stress test.

Interest is charged on whatever balance remains, and early on that balance is at its largest — so the interest portion of a fixed payment is highest in the first years and falls steadily as the balance reduces, even though the payment itself doesn't change.

It's usually a guaranteed, risk-free return equal to your mortgage rate, but check your mortgage terms first — many fixed-rate deals only allow a penalty-free overpayment up to a limit (commonly 10% of the balance per year, and one-off lump sums count toward the same limit) and charge an early repayment charge above that.

The extra monthly overpayment is added to every payment for the rest of the mortgage. A one-off repayment (e.g. a bonus or inheritance) is applied just once, straight off the balance, in whichever month you choose — you can add several to model repayments in different years. Both go straight to principal and both count toward your lender's penalty-free overpayment allowance.

Turn on "Rate changes after an initial period" in Advanced options and enter how many months your fix lasts and the rate you'll move to afterwards. The payment for that second stage is recalculated on your remaining balance and remaining term, the way a real remortgage or reversion to SVR works — not just the old payment at a new rate.

Loan-to-value is your loan as a percentage of the property price — shown when you enter a property price and deposit instead of a loan amount directly. Lenders price mortgages in LTV tiers: a smaller loan relative to the property price (a bigger deposit) usually unlocks meaningfully better rates, so it's worth knowing where you land even though it doesn't change the payment figures here directly.

Your required payment only covers interest, so the balance you borrowed doesn't reduce on its own — you still owe the full original amount at the end of the term. Lenders require you to show a credible plan to repay that lump sum (savings, investments, or selling the property), and if that plan falls through, you could be forced to sell or remortgage under pressure. It's why interest-only is far less common for residential mortgages than it used to be, though it's still standard for many buy-to-let loans.