For most UK homebuyers the question is not the headline rate in isolation. It is how that rate turns into a monthly payment, and what happens when a fixed deal ends. A few worked examples make the effect concrete.
The effect of the rate
The table shows the monthly payment on a £250,000 repayment mortgage over 25 years at different interest rates. It is an illustration using standard mortgage arithmetic, not a quote.
| Interest rate | Monthly payment |
|---|---|
| 3% | £1,186 |
| 4% | £1,320 |
| 5% | £1,461 |
| 6% | £1,611 |
Each percentage point adds roughly £130 to £150 a month, and the move from 3% to 6% adds £425 a month, about £5,100 a year. A borrower who had budgeted for the lower figure has to find that money from somewhere.
The remortgage cliff
Most UK borrowers choose a fixed rate for two or five years, after which they move to a new deal or to the lender’s standard variable rate. That means the payment shock arrives on a known date.
Take someone who borrows £250,000 over 25 years at a 4% two-year fix, paying £1,320 a month. After two years the balance is about £237,900, with 23 years left. If they refinance at 5%, the new payment is about £1,452, an increase of around £130 a month. At 6% it is about £1,591, an increase of around £270 a month. Planning ahead for that date, by checking deals up to six months before the fixed rate ends and asking about the cost of changing deal, avoids drifting onto a higher standard variable rate.
Term and deposit change the picture
Lengthening the term lowers the payment but raises the total interest. At 5% on £250,000:
| Term | Monthly payment | Total interest over the term |
|---|---|---|
| 20 years | £1,650 | about £146,000 |
| 25 years | £1,461 | about £188,000 |
| 30 years | £1,342 | about £233,000 |
| 35 years | £1,262 | about £280,000 |
Stretching from 25 to 35 years saves about £200 a month, but costs roughly £92,000 more in interest if the rate stays the same. A longer term can be a useful way to stay within a budget, with the option to overpay when finances allow, as long as the lender permits overpayments without penalty within the deal’s limits.
Rates also depend on the loan-to-value ratio, the size of the loan against the property’s value. Lenders typically price in bands, with the best rates for borrowers with larger deposits, which is one reason the deposit affects affordability twice: it reduces the loan and can reduce the rate.
Fees matter too. A product fee added to the loan accrues interest for the whole term, so a “low rate with a high fee” deal can cost more than it appears. Comparing the total cost over the fixed period is the fairest test.
How lenders judge affordability
Lenders in the UK must assess whether a borrower can afford the mortgage, including whether they could cope with a rise in rates. Since 2022 the Bank of England’s Financial Policy Committee no longer recommends a specific interest-rate stress test, so each lender uses its own assumptions. The Committee also keeps a limit on the proportion of new lending at very high loan-to-income multiples, with the aim of limiting riskier lending across the market. In practice, this affects how much a lender will agree to lend, which can be lower than the amount that seems affordable at today’s rates.
Putting it together
When comparing homes, deals or the choice between buying and renting, it helps to run the figures at the current rate and at one or two points higher. If the higher figure is unmanageable, the budget is too tight. That framing sits alongside the broader rent-or-buy decision, where rate risk is one of several variables.
This is general information, not personalised mortgage advice. Illustrations assume a constant rate and standard repayment calculations; rates, fees and lending criteria vary. Your home may be repossessed if you do not keep up repayments on your mortgage.
Sources: Bank of England Financial Stability Reports and Financial Policy Committee records on mortgage affordability; Financial Conduct Authority mortgage rules (MCOB); UK Finance mortgage market data; payments calculated by Finance Reporter using the standard amortisation formula.
