Britain caps the lender's book, not your ratio
The British case is the one most worth dwelling on, because the famous number is not a rule about you at all. The 4.5 times figure limits how much of a lender's new residential lending may sit at or above that multiple, and the Financial Policy Committee set that share at 15% when it introduced the limit in 2014. It has since been loosened at the level of the individual firm: from July 2025 the Prudential Regulation Authority has let a lender go beyond its own 15% by consent while aiming to hold the market aggregate at 15%, and a formal rule change was consulted on in 2026. Individual lenders will lend a borrower more than 4.5 times, particularly a high earner, and some go to 5.5 times. What actually decides a British application is an affordability stress test at a higher interest rate.
That makes the ratio on this page a description rather than a decision. There is no published British debt-to-income limit for a borrower to pass, so the 45% shown here is a market convention: it is roughly where lenders' own affordability assessments start to fail, not a line the Financial Policy Committee drew.
Income is assessed before tax, and the stress test is where most borderline applications are settled. A lender takes your income, subtracts committed expenditure and a figure for household costs, then checks whether the mortgage would still be payable at a rate materially above the one you are being offered. A borrower who clears 4.5 times income comfortably can still fail that test, and a borrower who fails it will not be rescued by a good ratio.
Gross household income of £60,000 a year reaches 4.5 times at
£270,000 of borrowing, the point from which a loan starts counting towards the lender's limited share. The lender's own stress test, applied to your existing car payment, card minimums and childcare, is what turns that ceiling into an actual offer, and it is usually the smaller of the two numbers.