Mortgage Affordability Calculator

What this calculator does. It estimates the maximum mortgage you could comfortably afford, and adds your deposit to suggest a realistic property price to target. Unlike pure income-multiple tools, it works from affordability — what's left of your income after debts, and how much of that you're willing to commit to housing.

How the calculation works. We start with your gross monthly income and subtract your existing monthly debt payments (car finance, credit cards, student loans). Your chosen comfort ratio — the share of remaining income you're happy to spend on the mortgage — gives a target monthly payment. We then reverse the standard repayment formula at your interest rate and term to find the largest loan that produces that payment. Adding your deposit gives the property price.

A worked example. Take a household earning £60,000 a year (£5,000 a month) with £200 of monthly debt payments, a £30,000 deposit, a 5.5% interest rate, a 25-year term and a 35% comfort ratio. Affordable monthly housing budget: 35% × £5,000 − £200 = £1,550. At 5.5% over 25 years that supports a mortgage of around £252,000, so with the deposit you could target a property around £282,000.

Why this matters. Knowing your realistic ceiling before viewing properties stops you falling for places you can't sustainably afford, and gives you a clear brief for estate agents and brokers. It also lets you stress-test the decision: re-run the calculation 1–2% above your offered rate and check the result still fits — that's roughly how UK lenders test affordability since the 2014 mortgage rules.

When to use it / when not to. Use it in early planning, before applying for an Agreement in Principle, and whenever your income, debts or rate expectations change. Don't treat the result as a guaranteed offer — lenders also look at credit history, employment type, deposit source and the property itself.

Common mistakes. Entering net (take-home) income instead of gross; forgetting to include credit card minimum payments and car finance; using today's low rate without stress-testing for rises; and ignoring running costs like service charges, ground rent and insurance, which sit on top of the mortgage payment.