The number a mortgage lender will give you depends on a combination of your income, your outgoings, the property price, and the lender's own risk appetite. Here is how the maths works.

Income multiples: the starting point

Most lenders start by applying an income multiple to your gross annual salary. The most common multiples are (you can model your own with the Mortgage Affordability Calculator):

• 4× income — a conservative baseline used by some lenders, particularly for higher-risk borrowers
• 4.5× income — the most common standard multiple across high-street lenders
• 5× or more — available from some lenders for higher earners (typically above £60,000–£75,000), certain professions (doctors, solicitors, accountants), or where affordability assessment is particularly strong

On a single £40,000 income, this produces a range of £160,000–£200,000. On £60,000, it is £240,000–£300,000. With a joint income of £80,000, 4.5× gives £360,000.

Income multiples are a ceiling, not a guarantee. The actual amount offered may be lower, depending on the affordability assessment below.

Affordability assessment: what lenders actually look at

Since the Mortgage Market Review (MMR) in 2014, all regulated mortgage lenders in the UK must conduct an affordability assessment — not just apply an income multiple. This means looking at:

• Committed expenditure — existing loan payments, hire purchase, credit card minimum payments, child maintenance
• Essential expenditure — utilities, food, childcare, council tax, insurance
• Basic quality of living costs — an estimate based on ONS expenditure data

What remains after all these costs must comfortably cover the mortgage payment. A borrower with a high income but substantial existing debts may be offered less than the income multiple would suggest.

Stress testing

Lenders also stress-test the mortgage at a higher rate than you will actually pay — to check you could still afford it if rates rose. The Financial Policy Committee removed the mandatory 3% stress test in August 2022, but most lenders continue to apply their own internal stress tests, typically checking affordability at 7–8% or the product rate plus 2–3%, whichever is higher.

A mortgage at 4.5% today would typically be stress-tested at 7–7.5%. Use the Mortgage Calculator to see what your monthly payments would look like at different rates. If you cannot afford payments at the stress rate, the lender will reduce the amount offered.

Deposit and LTV

The size of your deposit directly affects both the maximum you can borrow and the rate you will be offered. Lenders price by Loan-to-Value (LTV) band:

• 60% LTV (40% deposit) — best available rates
• 75% LTV (25% deposit) — competitive rates
• 85% LTV (15% deposit) — reasonable selection of products
• 90% LTV (10% deposit) — limited lenders, higher rates
• 95% LTV (5% deposit) — available through Mortgage Guarantee Scheme or select lenders, highest rates

A larger deposit does not increase the maximum loan amount — that is determined by income — but it reduces the LTV and therefore the rate, which affects what you can afford each month.

Joint mortgages

With a joint mortgage, lenders typically use the combined income to calculate the multiple. However, a few important points:

• Both applicants are jointly and severally liable — the lender can pursue either party for the full debt
• Both credit histories are assessed — a poor credit record on one applicant can affect the offer
• Some lenders weight the incomes differently (e.g. 1× the lower income plus 4.5× the higher) rather than simply applying a multiple to the combined figure