How do lenders actually decide how much I can borrow?

Most UK mortgage lenders start with a simple income multiple before anything else gets layered on top. The standard figure widely used across the high street is 4.5 times your gross annual income, or your combined gross income if you're applying jointly with a partner (FCA Mortgage Lending Statistics, 2026). It's the figure our calculator uses for the "standard" estimate, and it's a sensible first checkpoint before you start viewing property.

Take a salary of £40,000. At 4.5×, that gives a maximum loan of roughly £180,000, working out at around £1,008 a month over 25 years at 4.57% (Moneyfacts, July 2026, best-buy 2-year fixed). Run that figure through our mortgage repayment calculator to see how it changes at different rates or terms.

If your target property is close to or below your 4.5× figure, you're already in realistic territory. If it's well above, you need to know that now, not after you've made an offer.

What's the 5.5x higher multiple, and can I actually get it?

A small number of lenders will stretch to 5.5 times income, but it isn't something you can assume you'll qualify for. It tends to be reserved for higher earners, certain professions, or specific mortgage schemes, and the exact criteria vary considerably from lender to lender. Always confirm eligibility with a broker or lender directly rather than treating it as a default option.

On that same £40,000 salary, 5.5× would in theory unlock about £220,000 (£40,000 more than the standard multiple) at roughly £1,232 a month rather than £1,008. That's a meaningful jump in monthly commitment for a figure that isn't available to everyone who applies for it.

Treat the 5.5× number as "possibly available with the right lender", not as money you can count on when you're setting your search budget.

Why does my existing debt matter more than the headline multiple?

The multiple is only ever the opening bid. Every lender then stress-tests your income against your actual outgoings: car finance, credit cards, student loan repayments, buy-now-pay-later balances, childcare costs, even how many dependants you have, plus what your repayments would look like if rates rose. None of that shows up in the simple 4.5×/5.5× figures above, which is the single biggest limitation of any calculator like this one, ours included.

Someone on £45,000 with no debt and modest outgoings might be offered close to the full 4.5× figure. Someone on the same £45,000 with a £300 monthly car finance payment and £400 of credit card repayments could see their real offer come in £30,000-£50,000 lower once the lender's stress test is applied.

If you're carrying meaningful monthly debt, use the multiple as a ceiling rather than an expectation, and don't commit to a purchase price that only works if the lender ignores it.

Joint income example

Combined income of £83,000 (£38,000 + £45,000) gives a standard estimate of roughly £373,500 (4.5×) and a higher estimate of roughly £456,500 (5.5×). At 4.57% over 25 years, that's approximately £2,091 a month on the standard figure and £2,555 a month on the higher one, a gap of £464 a month. Existing debt, credit history and the lender's own stress test will ultimately decide whether you can service it.

How does my deposit change the picture?

The income multiple tells you the loan size a lender might offer. Your deposit determines the loan-to-value band that loan falls into, and LTV is what actually decides which rates you're offered: the lower your LTV, the better the rate typically available, which changes your monthly payment quite apart from anything to do with income (Moneyfacts, July 2026).

A first-time buyer building a deposit through a Lifetime ISA can check the government bonus using our LISA bonus calculator, and anyone budgeting for a purchase should run the price through our Stamp Duty calculator before assuming the loan amount is the only cost they need to find.

A bigger deposit gets you over the line and can shrink your monthly payment on the exact same loan size, so it's worth delaying a purchase to build one if the maths supports it.

What this means for you

If the standard 4.5× figure already covers the property prices you're looking at, treat that as your realistic starting point and plan around it. If you're in this position where 4.5× falls short of what you need and you're tempted by the higher multiple, the maths points toward speaking to a whole-of-market broker before you fall in love with a property that assumes it. They can tell you within a day or two which lenders might stretch further for your specific income, debts and deposit, and whether a Decision in Principle at that level is realistic. Most people who run these numbers end up needing that Decision in Principle to know their true position, because a calculator estimate is the opening conversation, not the final answer.

Use the figures above to set a realistic search range, then get a Decision in Principle before you start making offers on property near the top of it.