UK Mortgage Repayment Calculator
Work out your monthly mortgage payment on repayment or interest-only, the total interest over the term, and how much a regular overpayment saves in interest and years.
| Total interest over the term | — |
|---|---|
| Total repaid | — |
| First payment: interest / capital | — |
| If the rate rises by 1% | — |
Balance at the end of each year
In short
A UK repayment mortgage's monthly payment is P × r × (1+r)^n ÷ ((1+r)^n − 1) with r the monthly rate and n the months: £250,000 at 4.5% over 25 years is about £1,390 a month with £166,900 total interest. Interest-only pays just P × r (£938) and leaves the capital owed. Overpaying £200 a month clears that loan about 5 years early and saves roughly £38,500.
Who this is for: UK home buyers and remortgagers checking monthly payments, the cost of a fix, and what overpayments save.
How mortgage repayments are calculated
A repayment mortgage charges interest on the outstanding balance each month and sets a fixed payment that clears the balance exactly at the end of the term: payment = P × r × (1+r)^n ÷ ((1+r)^n − 1), where r is the monthly rate and n the number of months. Early payments are mostly interest; the split shifts towards capital as the balance falls, which is why the year-by-year table matters more than the headline figure.
- Interest-only pays just P × r each month; the capital must be repaid from savings, investments or the sale of the property.
- Overpayments go straight to capital. Most UK lenders allow 10% of the balance per year without an early-repayment charge during a fixed period.
- Fixed period: when a 2- or 5-year fix ends you move to the lender's standard variable rate (typically 2–4 points higher) unless you remortgage; the "rate rises by 1%" line shows the sensitivity.
- Lenders stress-test affordability at a higher rate than the product rate — see our affordability calculator for how much you can borrow.
See also: UK Stamp Duty (SDLT) Calculator.
Assumptions
- Monthly compounding; payment from the standard amortising formula; overpayments simulated month by month until the balance clears.
- Interest-only pays balance × monthly rate.
- Fees are not added unless you include them in the loan amount; the stress line re-prices at +1 percentage point.
Worked example
Monthly payment = £1,390; total interest £166,874. First month: £938 interest, £452 capital.
With a £200 overpayment the mortgage clears in about 19 years 11 months, saving around £38,500 in interest. A 1-point rate rise would push the payment to about £1,535.
Frequently asked questions
Is it better to overpay or shorten the term?
Overpaying gives the same interest saving as a shorter term but keeps the flexibility to stop; a formally shorter term commits you to the higher payment. Check your lender's 10% annual overpayment allowance first.
Why is my first year's balance barely lower?
At 4.5% over 25 years about two-thirds of the first year's payments are interest. The capital share rises every month; by year 15 it is more than half.
Does the calculator include fees?
No. Arrangement fees (often £999–£1,999) added to the loan increase both the balance and the interest; enter them in the mortgage amount to see the effect.
What is the difference between APRC and the rate?
APRC spreads fees and the reversion rate over the full term; the rate here is the product rate on which your monthly payment is based.
How much is a £250,000 mortgage per month?
About £1,390 at 4.5% over 25 years, £1,252 at 3.5%, or £1,535 at 5.5%.
How much does overpaying £100 a month save?
On £250,000 at 4.5% over 25 years, roughly £22,000 of interest and nearly 3 years off the term.
Related calculators
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