By Tim King · Updated 7 October 2026

Mortgage Repayment Calculator UK

Monthly Repayments on Repayment or Interest-Only Mortgages, With Overpayments

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Mortgage amount

Interest rate (% per year)

Mortgage term (years)

Repayment frequency

Overpayment per month (optional)

Offset balance (optional)

Repayment type

Schedule

Result

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How the UK Mortgage Repayment Calculator works

This mortgage repayment calculator UK version gives the monthly payment in pounds for a repayment or an interest-only mortgage. Enter the amount, the rate and the term and the monthly repayment appears with the total interest over the full term. Switch to interest only to see the lower monthly payment and the balance still owed at the end, add a monthly overpayment to see the interest it saves and the years it takes off, and read the amortisation schedule beneath the result.

A mortgage is usually the largest debt a UK household takes on. What makes the UK different is that the rate is almost never fixed for the whole term. You fix for two or five years, the deal ends, and you remortgage or fall onto the lender's standard variable rate. This calculator uses one rate for the whole term, so read its total interest as a way to compare scenarios at today's rate, not as a forecast.

How the mortgage repayment calculator UK lenders use works

A capital-and-interest mortgage is an annuity: the same payment every month, worked out so the balance reaches exactly zero on the last one. The formula is

payment = P × r ÷ (1 − (1 + r)^−n)

where P is the amount borrowed, r is the annual rate divided by the number of payments a year, and n is the total number of payments. Each month the lender charges interest on what you still owe, and whatever is left of the payment reduces the capital.

Example: the default figures. Borrowing £250,000 at 4.8 % over 25 years costs £1,432.49 a month. Over the term you pay £179,747.72 in interest, so £429,747.72 in all. In year one, £11,884 of the payments is interest and only £5,306 is capital. The two cross between years 11 and 12, and after that each year clears the loan faster than the last.

Example: interest only. The same loan on interest only costs exactly £1,000 a month, which is 4.8 % of £250,000 divided by twelve. After 25 years you have paid £300,000 in interest and still owe the full £250,000.

How many pounds a month per £100,000?

Monthly repayment per £100,000 borrowed, capital and interest, by rate and term

Rate	25 years	30 years	35 years
2.00%	£423.85	£369.62	£331.26
2.25%	£436.13	£382.25	£344.24
2.50%	£448.62	£395.12	£357.50
2.75%	£461.31	£408.24	£371.03
3.00%	£474.21	£421.60	£384.85
3.25%	£487.32	£435.21	£398.94
3.50%	£500.62	£449.04	£413.29
3.75%	£514.13	£463.12	£427.91
4.00%	£527.84	£477.42	£442.77
4.25%	£541.74	£491.94	£457.89
4.50%	£555.83	£506.69	£473.26
4.75%	£570.12	£521.65	£488.86
5.00%	£584.59	£536.82	£504.69
5.25%	£599.25	£552.20	£520.74
5.50%	£614.09	£567.79	£537.02
5.75%	£629.11	£583.57	£553.50
6.00%	£644.30	£599.55	£570.19
6.25%	£659.67	£615.72	£587.08
6.50%	£675.21	£632.07	£604.15
6.75%	£690.91	£648.60	£621.42
7.00%	£706.78	£665.30	£638.86

Scale a row by what you borrow. A £320,000 mortgage at 4.5 % over 30 years is 3.2 × £506.69, about £1,621 a month. Stretching from 25 to 35 years cuts the payment by roughly a sixth, but at 4.5 % it adds about £32,000 of interest per £100,000 borrowed.

Reading the result

Repayment is the scheduled amount per month, fortnight or week. UK lenders almost always collect monthly.
Total interest is every interest charge over the term at the rate you entered.
Total repaid adds the amount borrowed back on. On interest only this line becomes Still owing at end of term, the sum your repayment plan has to produce.
Interest saved and Paid off sooner appear once you enter an overpayment or an offset balance, measured against the same loan without either.

The amortisation schedule underneath splits each year, or each payment, into capital paid, interest paid and the balance left.

Overpayments and the 10 % allowance

Most fixed and tracker deals let you overpay up to 10 % of the balance each year without an early repayment charge. Go over it during the deal and the charge is typically 1 % to 5 % of the excess, falling each year of the fix. On the default loan, £150 a month extra saves £33,555.08 in interest and clears the mortgage 4 years and 1 month early. That is £1,800 a year, well inside the allowance. The calculator applies the overpayment for the whole term, so if you only overpay during a two-year fix the saving will be smaller.

Offset mortgages

With an offset mortgage, savings held with the lender are set against the balance before interest is charged, while the payment stays the same. Keeping £20,000 in the offset account on the default loan saves £40,901.82 and ends the mortgage 2 years and 4 months early. The savings earn no interest, so compare the saving with what the money would earn after tax in a normal account, at your own rate. Offset deals usually cost a little more than the standard version.

Tips and pitfalls

Include fees in the amount. Product fees of £999 or more are often added to the loan and then charged interest for 25 years. Paying them upfront is usually cheaper.
Test a higher rate. Lenders check affordability at a rate above the one you will pay. Try your figures two points higher to see what a remortgage at a worse time would cost.
Stamp duty, legal fees, surveys and insurance are not in these figures. Stamp duty land tax in England and Northern Ireland, and its Scottish and Welsh equivalents, is paid in cash at completion, and the bands change; check the current rates on GOV.UK.

For the same maths in other markets, see the US mortgage calculator and the Australian mortgage calculator. For car and personal loans, use the loan calculator, and to see what overpayments could earn if saved instead, try compound interest.

Sources: Mortgage calculator formula; MoneyHelper mortgage calculator.

Checked against: £200,000 at 5% over 25 years = £1,169.18 a month

FAQ

Why is the total interest so different from the monthly payment times the term?

It is not — the total repaid is exactly the payment times the number of months, and the total interest is that figure less the amount borrowed. On a 25-year mortgage the interest is usually around 70% of the amount borrowed at today's rates, which is the number that surprises people.

How much can I overpay without an early repayment charge?

Usually 10% of the outstanding balance per year during a fixed or discounted period, though some lenders measure it against the original balance and a few allow 20%. Check the mortgage offer. Once you are on the standard variable rate there is normally no cap.

What is an early repayment charge?

A penalty for repaying more than the allowance during the deal period, charged as a percentage of the amount overpaid, commonly 5% in the first year of a five-year fix stepping down to 1% in the last. It is designed to recover the lender's cost of funding the fixed rate.

Is stamp duty included in the mortgage?

No. Stamp duty land tax is paid to HMRC at completion and cannot be added to the mortgage. It is zero below a threshold that changes with policy and rises in bands above it, with a surcharge for additional properties. Budget for it from savings alongside the deposit and fees.

Does the calculator handle a fixed rate ending?

Not directly. It assumes one rate for the whole term. To see the effect of a rate change at the end of a fix, run the calculator once at the fixed rate, read the balance at the end of the fix from the schedule, and run it again with that balance, the new rate and the remaining term.

How do I calculate an interest-only mortgage in the UK?

Multiply the mortgage by the yearly rate and divide by 12. £250,000 at 4.8% is £1,000 a month interest only, against about £1,432 on a repayment mortgage over 25 years. Switch the calculator to interest only to see the full term.

Is interest only cheaper?

The monthly payment is lower, but the total cost is higher because the balance never falls. On the example, interest only costs £120,000 more in interest over 25 years than a repayment mortgage and still leaves £250,000 to find at the end.

How much can I borrow for a mortgage in the UK?

Most lenders cap the loan at 4.5 times gross annual income, with a few stretching to 5.5 times for higher earners or larger deposits, and then check the monthly payment against your outgoings at a stressed rate. Enter the amount that rule gives you here to see whether the payment fits your budget before approaching a broker.

Is a 35-year mortgage a bad idea?

It lowers the monthly payment but raises the total interest sharply: the £250,000 example costs about £86,900 more in interest over 35 years than over 25. Many borrowers take the longer term for affordability and then overpay within the 10% allowance, which gets the interest back down without committing to a higher contractual payment.