Mortgage Repayment Calculator

How this calculator works

Enter the amount you want to borrow, the interest rate, the term and the type of mortgage. The calculator converts the yearly rate to a monthly rate (the rate divided by 12) and then:

• Repayment mortgage: uses the standard amortisation formula to find one fixed monthly payment that clears both interest and the amount borrowed by the end of the term.
• Interest-only mortgage: the monthly payment covers only the interest on the amount borrowed. The full loan is still owed at the end of the term, so you need a separate plan to repay it.

If you add a monthly overpayment, the calculator models it month by month. Each overpayment reduces the balance, so less interest is charged afterwards. For a repayment mortgage it shows how much sooner the mortgage would be cleared and the interest saved; for an interest-only mortgage it shows how much of the balance would be left at the end.

Worked examples

All figures were produced by this calculator.

Example 1: £200,000 repayment mortgage at 4.5% over 25 years

The monthly payment is £1,111.66. Over 300 payments you would pay £333,499.49, of which £133,499.49 is interest, assuming the rate stays the same for the whole term.

Example 2: the same mortgage with £200 a month overpaid

Paying £1,311.66 a month clears the mortgage in 18 years 11 months instead of 25 years. Total interest falls to £97,219.09, a saving of £36,280.40.

Example 3: £150,000 interest-only at 5% over 25 years

The monthly payment is £625, and £150,000 is still owed at the end. Over 25 years the interest totals £187,500. If £300 a month is overpaid on top, the calculator shows the loan cleared in 22 years 7 months, because the overpayments gradually repay the capital.

Assumptions and what this calculator does not cover

• One rate for the whole term: most UK mortgages have an initial fixed or tracker deal for a few years, after which the rate changes. The calculator does not model a change of rate; re-run it with the rate you expect after the deal ends.
• Overpayment limits and charges: many fixed and tracker deals allow you to overpay up to a set amount each year (often a percentage of the balance) without an early repayment charge. Check your mortgage offer before overpaying.
• How the lender applies overpayments: the calculator assumes overpayments reduce the balance straight away and the monthly payment stays the same. Some lenders reduce the payment instead.
• Fees: arrangement, valuation, broker and legal fees are not included, and neither is Stamp Duty.
• Part-and-part mortgages, offset mortgages and buy-to-let: not modelled.

Using the result

Lenders look at affordability, not just the payment. Check that the monthly figure fits your budget with room to spare, and test it at a higher rate in case rates have risen when your deal ends. Mortgage rates tend to move with Bank Rate and wider market conditions. To estimate how much you might be able to borrow, see the mortgage affordability calculator, and for the upfront tax on a purchase in England or Northern Ireland use the Stamp Duty calculator. For more on how interest and capital change over time, read how loan repayments work.

If you are struggling to keep up with mortgage payments, contact your lender as early as possible to discuss options. Mortgage payments are a priority debt because the loan is secured on your home. Some people receiving certain benefits may be able to get help through Support for Mortgage Interest, which is a loan from the government; GOV.UK explains who can apply. Free, confidential debt advice is also available.

Frequently asked questions

What is the difference between a repayment and an interest-only mortgage?

With a repayment mortgage, each payment covers interest and part of the loan, so it is fully repaid by the end of the term. With interest-only, payments cover only the interest and the whole loan must be repaid at the end from savings, investments or the sale of the property.

How much can overpaying save?

It depends on the rate, the balance and how long is left. In the example above, overpaying £200 a month on a £200,000 mortgage at 4.5% saves over £36,000 of interest and clears it about six years early, assuming the rate does not change.

Will overpaying trigger an early repayment charge?

It can, if you overpay more than your lender allows during a fixed or discounted deal. Many lenders allow a set amount each year without a charge. Check your mortgage offer or ask the lender.

Does a longer term cost more?

Usually. A longer term lowers the monthly payment but increases the total interest, because the balance is outstanding for longer.

Is the rate I enter the same as the APRC?

Not necessarily. The APRC includes fees and assumes you move to the lender's standard variable rate after the initial deal. Use the rate for the period you want to model.

Sources

• Bank of England: Interest rates and Bank Rate
• GOV.UK: Stamp Duty Land Tax – residential property rates
• GOV.UK: Support for Mortgage Interest

Rates for tax year 2026/27, last reviewed October 2026.

Results are estimates for planning, not financial or tax advice. See our terms and methodology.