How Mortgage Affordability Is Assessed (2025/26)
Mortgage affordability determines how much a lender will let you borrow. It is not simply a multiple of your salary — lenders run detailed income verification, credit stress tests, and affordability calculations that factor in your outgoings, dependants, and interest rate sensitivity. Knowing the methodology helps you predict approval and manage expectations.
The Two Key Tests
1. Loan-to-Income (LTI) Multiple
Most lenders cap borrowing at 4–4.5× single income or 3.5–4× joint income. The Bank of England requires that no more than 15% of a lender's new mortgages exceed 4.5× income.
| Income | 4× Multiple | 4.5× Multiple |
|---|---|---|
| £35,000 (single) | £140,000 | £157,500 |
| £50,000 (single) | £200,000 | £225,000 |
| £60,000 + £30,000 (joint) | £360,000 | £405,000 |
| £80,000 + £50,000 (joint) | £520,000 | £585,000 |
2. Affordability / Stress Test
Lenders test that you could still afford repayments if rates rose by typically 2–3%. The FCA removed prescriptive stress test requirements in 2022, but lenders continue to apply their own — most still test at SVR + 1–2%.
Stress Test Rate = Your offered rate + Lender stress buffer (typically 2–3%) Example: 5% mortgage rate → tested at 7–8% Monthly payment at 5% on £250,000 (25y): £1,461 Monthly payment at 8% on £250,000 (25y): £1,929 Lender checks your income/outgoings can absorb £1,929/month.
What Counts as Income
| Income Type | Typically Accepted? | At What %? |
|---|---|---|
| Employed basic salary | Yes | 100% |
| Regular bonuses (evidenced) | Usually | 50–100% |
| Overtime (regular) | Usually | 50–75% |
| Self-employed profits | Yes (2–3yr average) | 100% of average |
| Rental income | Yes | 70–100% |
| Benefits (DLA, PIP etc.) | Some lenders | 100% if accepted |
| Investment income | Some lenders | 100% if evidenced |
What Affects the Maximum Loan
- Credit score — impacts rate offered, not directly the multiple, but a poor score may mean lower LTI access
- Deposit size — higher LTV (lower deposit) means higher rate, reducing max loan via affordability test
- Committed outgoings — car finance, credit cards, child maintenance, childcare all reduce affordability
- Term length — longer term reduces monthly payment, increasing the amount you pass affordability at
- Number of dependants — increases assumed living costs, reducing headroom
What-If Scenarios
Scenario 1: Impact of car finance on borrowing capacity
£350/month car finance reduces monthly disposable income by £350. At typical affordability ratios, this can reduce maximum mortgage by £50,000–£80,000. Clearing car finance before applying can materially increase borrowing capacity.
Scenario 2: Extending the term from 25 to 35 years
Extending the term lowers monthly payments, which can help pass the affordability test. £250,000 mortgage at 5%: 25y = £1,461/month; 35y = £1,264/month. But total interest paid rises by ~£60,000.
Scenario 3: Raising the deposit from 5% to 20%
On a £300,000 property: 5% deposit (£15,000) → likely 5.5–6% rate. 20% deposit (£60,000) → likely 4.5–5% rate. Lower rate means lower stress test threshold and improved affordability — allowing a larger loan at the same income.
Frequently Asked Questions
→ Calculate your maximum borrowing with the Mortgage Affordability Calculator
Indicative only. Each lender has different criteria. These figures reflect typical UK high street lender practice in 2025. Always obtain a Decision in Principle before making an offer.