What is a repayment mortgage?
A repayment mortgage is the usual UK home loan. Each monthly payment covers the interest and a slice of the amount you borrowed, so the balance falls to zero by the end of the term if you keep up the payments. On a fixed rate the monthly amount stays the same, but early payments are mostly interest and later payments are mostly capital.
A longer term cuts the monthly payment and increases the total interest, because the balance stays higher for longer. Stretching from 25 to 35 years can cut the monthly cost by about 15–20% and roughly double the interest. This calculator assumes the rate you enter lasts for the whole term. Most UK deals are fixed for 2–10 years, then the rate changes.
A £200,000 UK repayment mortgage at 4.6% over 25 years costs £1,123 per month and £136,914 in total interest over the term.
How repayment mortgages work
Same monthly, different split
Every month you pay the same amount. Early on most of it is interest; by the end most of it is capital. That's why overpayments in the first half save dramatically more interest than in the last half.
Term trade-off
Extending from 25 to 35 years cuts your monthly by 15–20% but roughly doubles the total interest. Only extend if affordability genuinely requires it.
Frequently asked questions
How is a UK mortgage repayment calculated?
Using the standard amortisation formula: Monthly = loan × (r × (1+r)^n) / ((1+r)^n − 1), where r is the monthly rate and n is total months. You pay the same amount each month; interest proportion falls, capital proportion rises.
Why does a longer term cost more in total?
Total interest scales with the years you hold the debt. A £200k mortgage at 4.6% costs about £123k interest over 25 years, or £166k over 35 years — with only ~£170/month saved on the monthly payment.
Does the rate apply for the whole term?
In the UK, almost always no. You fix for 2, 3, 5 or 10 years, then revert to the lender's SVR. Most borrowers remortgage onto a new fix to avoid the SVR. This calculator projects as if the rate held for the full term.
Is capital-and-interest cheaper than interest-only?
The monthly payment is higher, but you clear the debt. Interest-only has lower monthly cost but the full balance is still owed at the end — you need a separate repayment plan.
How much more am I paying vs rate of interest alone?
At 4.6% over 25 years, total interest is around 60% of the original loan. Push the rate to 6% and it approaches 90%. Sharp rates compound over time.
Reviewed by the Mortgage118 editorial team. Calculation assumes a fixed rate for the entire term — real-world UK mortgages typically fix for 2–10 years. Provides an estimate only.
- Type
- Capital & interest
- Rate treatment
- Fixed for term
- Payment timing
- End of month
Real-world rates change after your fix ends. Use the remortgage calculator for switching.