The Mortgage Affordability Calculator estimates how much you could realistically borrow in the UK, by combining the two checks most lenders actually use: an income-multiple cap and an affordability stress test. Enter your income (and a joint applicant's, if relevant), your monthly committed outgoings, your deposit and the property price you're considering, and the calculator works out both caps automatically. It then shows you the lower of the two — the figure a lender would be most likely to offer — along with the maximum property price your deposit and loan together could reach. If you're still weighing up whether buying makes sense at all, our Rent vs Buy Calculator can help you compare the two routes. All multiples, rates and ceilings used are clearly labelled as illustrative and fully adjustable, since real lender criteria vary considerably.
| Check | Result |
|---|
Lenders don't just multiply your salary by a fixed number — they run two separate checks and offer you whichever one gives the lower, more conservative figure. The first is a simple income-multiple cap; the second is an affordability stress test that looks at your actual committed outgoings and tests whether you could still afford the repayments at a higher interest rate than you're being offered today.
Based on your combined gross income, the calculator applies your chosen income multiple to get the first cap. It then works out your monthly committed-outgoings-adjusted affordability ceiling, and uses the standard repayment mortgage formula (inverted) at your chosen stress rate and mortgage term to work out the maximum loan you could service — the second cap. Your likely maximum loan is the lower of the two.
Your calculation summary will update here as you change the figures above.
This calculator uses illustrative, adjustable assumptions (a 4.5x income multiple, an 8% stress rate and a 45% affordability ceiling by default) to approximate how UK lenders typically assess affordability. Real lenders vary significantly in the income multiples, stress rates and outgoings assessments they use, and your actual offer will also depend on your credit history, employment type and the lender's own underwriting policy. This tool is provided for general guidance only and does not constitute financial advice — always get a decision in principle from a lender or speak to a qualified mortgage broker before making an offer on a property.
A mortgage affordability assessment is the process a UK lender goes through to decide not just whether you're eligible for a mortgage, but how much they're willing to lend you. Rather than relying on a single number, lenders combine at least two separate checks: a simple income-multiple cap (a multiple of your gross annual income), and a more detailed affordability check that looks at your actual monthly income after accounting for your committed debts, and tests whether you could keep affording the repayments even if interest rates rose. Whichever of these two checks produces the lower figure is generally the one that determines your actual maximum offer.
This calculator mirrors that two-check structure: it shows you an income-multiple cap, a stress-tested affordability cap, and then a "likely max loan" that takes the lower of the two — the figure closest to what a real lender assessment would be likely to produce.
An income multiple is simply your gross annual income (or combined gross income, for a joint application) multiplied by a fixed number to produce a starting loan ceiling. A commonly cited illustrative figure is 4.5x combined income, but this is not a universal rule — individual lenders set their own multiples, and these can range from around 3.5x up to 5x or even 5.5x depending on your income level, deposit size (loan-to-value), employment type, and the lender's own risk appetite. Higher earners, those with smaller loan-to-value ratios, or professionals in certain occupations are sometimes offered higher multiples by specific lenders.
Historically, the 4.5x figure has particular significance because of a 2014 Bank of England Financial Policy Committee recommendation limiting how much "high loan-to-income" lending (at or above 4.5x income) each lender could do as a share of their total new mortgage lending. That framework has itself been revised over time as regulators rebalance individual lender flexibility against overall market-wide risk, which is one reason you'll see mortgage multiples vary more between lenders than you might expect.
Under the FCA's Mortgages and Home Finance: Conduct of Business sourcebook (MCOB), specifically MCOB 11, UK mortgage lenders are required to assess whether a borrower can actually afford a mortgage — not just whether they're willing to sign up for it. Part of that assessment, for most variable-rate or short-fixed mortgages, involves testing affordability against the possibility of future interest rate rises, rather than only the rate on offer today. This exists to reduce the risk of borrowers being approved for mortgages they can only afford while rates stay low, and then falling into payment difficulty if rates rise.
The exact mechanics of this stress test have changed over time. The Bank of England's Financial Policy Committee withdrew its recommendation for a fixed stress-test margin (which had required lenders to test affordability at roughly 3 percentage points above a mortgage's reversion rate) with effect from August 2022, judging that lenders' own underwriting checks plus a separate market-wide loan-to-income safeguard gave sufficient protection without a single rigid rule. FCA rules under MCOB 11.6 still require lenders to account for likely future interest rate increases where relevant, but each lender now sets its own stress rate and margin, rather than following one government-mandated percentage — which is why this calculator treats the stress rate as an adjustable, illustrative input rather than a fixed figure.
Committed outgoings are regular, contractual payments you're obligated to make, separate from everyday living costs. Lenders typically include: existing loan repayments, credit card minimum payments (or a notional repayment on the full balance), car finance or lease payments, student loan repayments, child maintenance payments, and regular childcare costs. They're distinct from "basic essential expenditure" — council tax, utilities, food, insurance, travel and similar day-to-day costs — which lenders usually estimate separately, either from your bank statements or using modelled averages, even though you don't explicitly list them as a single input in this calculator.
Your deposit doesn't directly change either the income-multiple cap or the stress-tested affordability cap in this calculator — those are driven by income, outgoings and the assumptions you've set. What it does change is the maximum property price you can reach (your likely max loan plus your deposit), and in the real world, your deposit size also determines your loan-to-value (LTV) ratio, which strongly influences the interest rate you're offered. A larger deposit (lower LTV) typically unlocks a cheaper rate, which lowers your real-world stress-tested monthly payment and can, in practice, raise your affordability cap as well — an indirect effect this calculator doesn't automatically model, since you set your own stress rate.
If you're self-employed, a contractor, or earn significant variable income (commission, bonus, overtime), lenders typically want at least two years of accounts, tax returns (SA302s) or an accountant's certificate, and will often use an average of the last two or three years' income, or the lower of two years' figures, rather than your most recent or highest year alone. This can mean the income figure actually used in both the income-multiple and affordability checks is lower than your current or best-ever earnings — worth bearing in mind when entering a figure into this calculator if your income varies year to year.
When two (or occasionally more) applicants apply together, lenders combine their gross incomes before applying the income multiple, and combine both incomes and both sets of committed outgoings for the affordability stress test. This generally increases both caps compared with a sole application, which is why this calculator has a separate field for a joint applicant's income — simply leave it at £0 if you're applying alone. Bear in mind that a joint applicant's existing debts and outgoings are also added into the assessment, which can partly offset the benefit of their extra income.
Your credit history affects a mortgage offer in two distinct ways. First, it can affect which lenders will even consider you, and some lenders reserve their most generous income multiples or more flexible affordability criteria for applicants with the strongest credit files. Second, a weaker credit history typically means a higher interest rate — and because that rate feeds into your (real-world) stress-tested monthly payment, a higher rate can itself lower your affordability cap, even if your income and outgoings are unchanged. In other words, credit history can reduce how much you're offered, not just the cost of borrowing it.
Take a joint application with a combined gross income of £70,000, monthly committed outgoings of £300, a deposit of £25,000, a 25-year term, an illustrative 4.5x income multiple, an 8% stress rate and a 45% affordability ceiling. The income-multiple cap is £70,000 × 4.5 = £315,000. The affordability-ceiling monthly figure is (£70,000 ÷ 12 × 0.45) − £300 = £2,625 − £300 = £2,325 available per month. Solving the repayment-mortgage formula at 8% over 25 years for a £2,325 monthly payment gives an affordability-based cap of roughly £299,000. Because £299,000 is lower than the £315,000 income-multiple cap, the likely max loan here is around £299,000 — plus the £25,000 deposit, a maximum property price of roughly £324,000. Once you have a target price in mind, check the Stamp Duty Calculator (SDLT) to see the tax due on top of that purchase.
A longer mortgage term spreads the same loan amount over more monthly payments, which lowers the monthly payment needed to service any given loan size — and because the affordability stress test works backwards from "what monthly payment can you afford", a lower required monthly payment per £1 borrowed means a longer term generally increases your affordability-based cap. It doesn't change your income-multiple cap at all, since that calculation doesn't reference the term. The trade-off is that a longer term means paying interest for longer, so a higher affordability cap from a longer term isn't automatically the cheapest or best option overall.
Under MCOB 11.6, the requirement to stress-test against likely future interest rate rises generally doesn't apply in the same way if you're taking a mortgage rate that's fixed for 5 years or more (or for the full term, if shorter than 5 years) — because the rate, and therefore the payment, can't rise unexpectedly during that fixed period. Shorter fixed-rate deals and variable-rate mortgages are more likely to be stress-tested against a higher notional rate, since the payment could genuinely increase before the loan is repaid or you remortgage. This is one reason the stress rate used by real lenders can differ noticeably depending on the type of deal you're applying for.
Two separate pieces of UK regulation sit behind the figures used in this calculator. The 4.5x-style income multiple traces back to a 2014 Bank of England Financial Policy Committee recommendation that limited the share of each lender's new mortgage lending that could be extended at 4.5x income or more — a market-wide safeguard against excessive household debt, not a cap on any single borrower. The interest rate stress test traces back to FCA rules under MCOB 11, alongside a separate, now-withdrawn Financial Policy Committee recommendation for a fixed stress margin above a mortgage's reversion rate, withdrawn from August 2022 onward. Both frameworks have continued to evolve since, with regulators periodically rebalancing the flexibility given to individual lenders against overall market-wide risk — which is exactly why this calculator treats the multiple, the stress rate and the affordability ceiling as adjustable assumptions rather than fixed rules.