How lenders assess mortgage affordability, in plain English

A lot changed in 2014

Before the Mortgage Market Review, many lenders worked out what you could borrow using a simple income multiple: three or four times your salary, and that was largely that. The rules were light, and the checks were thin.

The Mortgage Market Review changed that. In 2014 the Financial Conduct Authority introduced rules that made affordability assessment a legal obligation, not a discretionary box to tick. Lenders moved from a rough income multiple to a detailed picture of your financial life. Those rules are now set out in the FCA's Mortgage Conduct of Business sourcebook, at section 11.6.

What MCOB 11.6 actually asks lenders to do

The responsible-lending rules in MCOB 11.6 require lenders to verify your income, assess your outgoings, and stress-test the repayment against future interest-rate rises. Each of those steps matters more than most borrowers realise.

Verify income. A lender cannot take your stated salary at face value. They must check it: payslips, P60s, employer references, tax returns for the self-employed. For some buyers this is straightforward; for others, income that does not show up cleanly on paper creates friction even when the money is genuinely there.

Assess outgoings. This is where MCOB 11.6 goes into real detail. Lenders are required to look at three categories of expenditure: committed spending (loan repayments, credit-card minimums, lease agreements); basic essential spending (utilities, food, travel, insurance, childcare); and basic quality-of-living costs (clothing, phone, socialising, subscriptions). Every category affects how much room is left for a mortgage repayment.

Stress-test the repayment. Lenders cannot simply check whether you can afford the mortgage today. They must check whether you could still afford it if interest rates rose. The precise stress rate varies by lender and product, but the principle is the same: a comfortable repayment now must remain manageable if borrowing costs move upward.

There is also a macro-level limit. UK regulators restrict how much new residential mortgage lending banks can do above 4.5 times a borrower's income. That cap does not mean every lender will lend to 4.5 times income; it means very few will go beyond it.

Why two people on the same salary can borrow different amounts

This is the question most buyers ask when a colleague or friend reports a very different outcome from their own.

Two households with identical gross incomes can have entirely different affordability profiles once a lender runs the numbers. Someone with a clean credit record, no outstanding loans, no dependants, and modest discretionary spending looks very different from someone with three active credit commitments, a car on finance, and school fees. The lender is not making a moral judgement; they are applying a formula that the regulator requires them to apply.

Employment type matters too. A salaried employee's income is simple to verify. A freelancer, a director paying themselves through dividends, or someone with multiple income streams requires more documentation and often more underwriting time. Some lenders price in that complexity; others decline it.

The property itself plays a role. Loan-to-value ratios change what is available. A buyer with a 30 per cent deposit will generally access different rates and lender appetite than one with a 5 per cent deposit, even if the underlying affordability is similar.

What this means if you are preparing

Many buyers find it useful to understand their spending picture before a lender looks at it, rather than after. The lender will categorise your outgoings into committed, essential, and quality-of-living buckets. If you can see how your own transactions map to those categories, the assessment becomes less of a surprise.

A broker may help you identify which lenders are most likely to treat your income and expenditure profile favourably. Lenders do not all apply the rules identically; within the regulatory framework there is genuine variation in appetite and interpretation. Understanding the landscape in advance can make that conversation more productive.

It can also help to understand what shows up in your transaction history that is temporary versus what is structural. A regular monthly commitment that ends in six months is treated differently from one with five years to run.

How Moxim approaches this

Moxim categorises every transaction in your connected accounts using a 151-category taxonomy mapped to MCOB 11.6 tiers, as an illustrative methodology, not a regulated MCOB assessment or a lending decision. The goal is to let you see your spending picture the way a lender's framework would organise it, before you sit down with a broker, using your own Open Banking data.

We showed this approach at the FCA Mortgages TechSprint 2025.

Everything Moxim shows today is illustrative and educational, never a quote, an offer, or a lending decision. Moxim is not yet PRA-authorised or FCA-regulated. If you would like to see where you stand, see the experience.