Online calculators multiply your income and call it affordability. Lenders do something more searching: they apply an income multiple as a ceiling, then interrogate your real outgoings and stress test the repayments against higher rates. This step estimates what you could borrow — and separately, what you should.
How lenders size a loan
The starting point is an income multiple, commonly around 4 to 4.5 times gross annual income (occasionally more for strong profiles). From that ceiling they subtract for committed outgoings: loans, card balances, childcare, maintenance payments, car finance. Two applicants' incomes combine, but so do their commitments. The affordability calculator applies these mechanics to your figures.
The stress test
Lenders check you could still pay if rates rose — typically modelling your repayments a few percentage points above the rate you are actually taking. If your budget only works at the introductory rate, the lender may decline, and more importantly the loan is genuinely unsafe. Run your own stress test before any lender does.
Maximum is not comfortable
The most a lender will give you and the most you can borrow while still saving, holidaying and absorbing a boiler failure are different numbers, often by tens of thousands. Decide your comfortable monthly payment first — anchored to what you currently pay in rent plus what you save — and derive your price ceiling from that, not from the lender's maximum.
Scenario: two incomes, one car loan
Sam earns £38,000 and Priya earns £30,000. They have a £310 monthly car payment and want to know their realistic budget.
At 4.5 times their combined £68,000 income, the theoretical ceiling is £306,000 of borrowing. But the car loan and their childcare costs reduce what lenders will actually offer — a broker estimates nearer £280,000. With their £34,000 deposit, that suggests a price around £310,000. Stress-testing at a higher rate, they find the monthly payment they are truly comfortable with points to borrowing £255,000.
Outcome: They set their search ceiling at £290,000 — below the lender maximum, above panic level — and know exactly which number moves if the car loan is cleared first. The gap between 'could borrow' and 'should borrow' became a deliberate choice instead of a surprise.
Your action list
Practical tips
- Clearing a small loan before applying can raise your borrowing capacity by more than the loan's balance.
- Anchor comfort to evidence: current rent plus current monthly saving is a payment level you have already proven you can sustain.
What can go wrong
- Borrowing to the ceiling leaves the whole budget exposed to a single rate rise, job wobble or baby.
- Affordability calculators (including ours) are guides — only a full application tests your actual file, and the answer can be lower.
- PropertySquares provides education, not financial or legal advice. Verify current rules and obtain advice for your circumstances before acting.