How the repayments are worked out
Repayment mortgages use the standard annuity formula, which spreads capital and interest into equal monthly payments:
Monthly payment = loan × r ÷ (1 − (1 + r)−n)
r = annual rate ÷ 12, n = years × 12
For £400,000 at 4.5% over 25 years: r = 0.00375 and n = 300, giving £2,223.33 a month. Over the full term you repay £666,999, so the interest comes to £266,999.
Interest-only
On interest-only you pay just the interest: £400,000 × 4.5% ÷ 12 = £1,500 a month. It is cheaper each month, but the £400,000 is still owed at the end, so lenders want a repayment plan.
Income you would need
Lenders usually cap borrowing at about 4 to 4.5 times income, with some going to 5 or 5.5 times for higher earners. To borrow £400,000 you would typically need a household income of £88,889 to £100,000. Check your figures with the mortgage affordability calculator.
Buying a home? Add the stamp duty to your budget, and see how much overpaying could save.
Frequently asked questions
How much is a £400,000 mortgage a month?
A £400,000 repayment mortgage costs about £2,223 a month over 25 years at 4.5% interest, £2,027 over 30 years and £1,893 over 35 years.
What salary do I need for a £400,000 mortgage?
Most UK lenders lend around 4 to 4.5 times income, so a £400,000 mortgage usually needs a household income of about £88,889 to £100,000 a year, depending on your debts and outgoings.
How much interest will I pay on a £400,000 mortgage?
At 4.5% over 25 years you would repay £666,999 in total, of which £266,999 is interest. A shorter term or a lower rate cuts this.
How much is a £400,000 interest-only mortgage a month?
At 4.5%, interest-only payments on £400,000 are about £1,500 a month, but you still owe the full £400,000 at the end of the term.
Last reviewed October 2026. Example rates only; your lender's rate, fees and term decide what you actually pay.