⚡ The short version
Enter the amount borrowed, the rate and the term. You get the monthly payment, the total interest, and — the number most calculators bury — what happens if you overpay. £250,000 at 4.5% over 25 years is £1,389.58 a month, with £166,874 of interest over the loan.
The calculator
How to use it
- Amount borrowed — price minus deposit, plus any fees you are rolling into the loan.
- Rate and term — the rate on your deal and how long you want to be paying, not the maximum the lender offers.
- Overpayment — try £100 or £200 a month and watch the term, not the payment. That single number usually decides whether overpaying is worth it.
Worked example
Borrow £250,000 at 4.5% over 25 years (300 payments). The monthly rate is 0.045 ÷ 12 = 0.00375, and the standard repayment formula gives £1,389.58 a month. Over 25 years you repay £416,874 in total — £166,874 of it interest.
Stretch the same loan to 30 years and the payment falls to £1,266.71 — but total interest rises to £206,017. Five extra years costs roughly £39,000 for a £123-a-month saving.
Overpay £200 a month on the 25-year loan and it clears in about 20 years instead of 25, saving roughly £38,500 in interest. Overpayments cut the term, not the payment.
What this calculator does not do
- Reversion rates. Most UK deals fix for 2–5 years then revert to the lender's variable rate. The payment shown is for the rate you enter.
- Fees and charges. Arrangement fees, valuation fees and early-repayment charges are not in the number unless you add them to the amount borrowed.
- Affordability. What you can borrow is the lender's decision (income multiples, stress tests, credit history) — this tool answers what a given loan costs, not whether you will get it.
🛠️ Related money tools
📖 Long-form companion: How mortgages really work.
❓ Frequently asked questions
How is a UK mortgage payment calculated?
Monthly payment = P × r × (1+r)^n / ((1+r)^n − 1), where P is the loan amount, r is the monthly rate (annual rate ÷ 12) and n is the number of monthly payments. On £250,000 at 4.5% over 25 years that is £1,389.58 a month.
Do overpayments reduce my payment or my term?
The term. Overpaying £200 a month on a £250,000 loan at 4.5% clears it in about 20 years instead of 25 and saves roughly £38,500 in interest. Most UK lenders allow 10% overpayment a year without charge during the fix.
How much interest do I pay over the life of the loan?
More than most summaries admit. £250,000 at 4.5% over 25 years costs £166,874 in interest; stretching to 30 years drops the payment by £123 a month but adds about £39,000 of interest.
Is this mortgage advice?
No. This is a calculator, not advice. It models fixed-rate capital-and-interest repayment; it does not know your credit file, the fees, or what rates will do next. For decisions that matter, speak to a qualified mortgage adviser.