Your home affordability budget is the maximum price you can borrow for a house while keeping mortgage and other debts affordable—use a home affordability calculator to get a quick figure. This article explains what the budget really means, where the numbers come from, and how you can check your own limit without guessing.
What the home affordability budget actually is
It isn’t the price of your dream home or the sum a bank will lend you outright. It’s the largest mortgage payment you can manage without your finances feeling the strain. Lenders mostly follow the 28/36 rule: no more than 28% of your gross monthly income on housing costs, and no more than 36% when you add in other debts like car loans or credit cards. That sets the cap on what you can borrow based on your income and commitments.
The calculations rely on your gross monthly income, your monthly debt payments, the interest rate you expect, the mortgage term, and your deposit. Lenders feed these into affordability formulas to estimate the biggest loan you can service without running into trouble. They also run stress tests—such as assuming a higher rate—to check if you could still cope if rates climbed.
A couple in Manchester earn £68,000 a year between them, so £5,667 gross a month. They pay £450 a month on car finance and credit cards, and can put down £30,000. At a 4.5% interest rate over 25 years, their maximum mortgage payment under the 28% rule is £1,587 (28% of £5,667). After deducting the £450 in debts, they have £1,137 left for the mortgage itself. Plugging that into a repayment calculator shows they could borrow roughly £215,000. Add the £30,000 deposit, and their ceiling for a home price is £245,000.
The rule doesn’t work well if your income changes month to month—freelancers or people on bonuses often get a lower limit than the calculator suggests. Some lenders are more generous, allowing up to 30% of income on housing, while others insist on 25%. A bigger deposit or a lower rate can push the loan amount up, but your income might still cap the affordability test.
Work it out yourself in four quick steps
- Enter your gross annual income before tax.
- Enter your total existing monthly debt payments.
- Enter the mortgage rate, term and your down payment.
- See the home price and monthly payment you can realistically support.
28/36 rule: housing ≤ 28% of gross income and total debts ≤ 36%, back-solved into a loanHome Affordability vs. Income & Debt Ratios
| Factor | 28/36 Rule | Example with $80k Income |
|---|---|---|
| Max housing cost (28%) | $1,867/month | $1,867/month |
| Max total debt (36%) | $2,400/month | $2,400/month |
| Remaining for other debts | $533/month | $600/month |
| Down payment (10%) | N/A | $20,000 |
| Estimated home price | N/A | $200,000 |
Why getting this wrong really hurts
Get the budget wrong and you’ll end up house-hunting out of your depth. That means struggling every month to meet the payments or selling in a hurry when it all becomes unsustainable. It’s not just about the bank’s approval—it’s about knowing you can sleep at night without the mortgage looming like a financial deadweight. Once you have the real figure, you can search homes you can truly afford, negotiate with certainty, and avoid the stress of overcommitting from day one.
Three real cases with the numbers laid bare
Standard couple in London
A couple earn £85,000 a year, so £7,083 gross monthly. They have £300 a month in student loans and no other debts. The 28% rule gives a £1,983 monthly budget for mortgage and insurance. After subtracting £300, £1,683 remains for the mortgage itself. At 4.25% over 30 years, that’s roughly £350,000 they can borrow. With a £50,000 deposit, they’re looking at a £400,000 home price limit.
Odd income and rounding trap
A freelancer takes home £4,123 a month after tax but declares £48,000 a year. The lender uses gross income, so £4,000 a month. They also have £250 a month in car finance. The 28/36 rule gives a £1,120 mortgage budget. After £250 in debts, £870 is left for the mortgage. At 4.75% over 25 years, the calculator shows £156,000. Rounding the monthly figure up to £875 adds £2,000 to the loan, so they’d borrow £158,000 instead—worth checking how the lender rounds their numbers.
The three most common slips to avoid
| Common mistake | What to do instead |
|---|---|
| Using net income instead of gross in the calculator. | Always use your gross monthly income—what you earn before tax and National Insurance—so the lender’s 28/36 test matches reality when they run their own checks. |
| Forgetting to include council tax, utilities, and insurance in the monthly housing costs. | Add those on top of the mortgage payment when you’re working out if you can truly afford the home; otherwise you’ll be scrambling for an extra £200 a month once you move in. |
| Mixing up years and months in the interest rate or loan term. | Double-check the units: a 4% interest rate is 0.333% a month if you’re using monthly calculations, not 4% a month—small slips can blow the whole budget out of proportion. |
Use our free home affordability calculator
| Tool | What it does |
|---|---|
| Home Affordability Calculator | Estimate the home price you can afford from your income, debts and down payment using the 28/36 rule. |
Try the Home Affordability Calculator
Skip the manual maths — enter your numbers and get the answer instantly.
Open the Home Affordability Calculator →One last check before you start looking
Small differences in interest rate, term or timing can add up to large sums over the years. Before committing to any financial decision, run a few different scenarios so you can see the full picture and choose with confidence.
The three things to remember
- Use gross monthly income, not net, when you run the numbers—lenders do.
- Add council tax, utilities, and insurance to the mortgage bill to see the full monthly cost.
- Round down the loan figure by 5–10% to leave breathing room for rate rises or life changes.
Frequently asked questions
What is the 28/36 rule?
It is a common lending guideline: spend no more than 28% of your gross monthly income on housing, and no more than 36% on all debt payments combined. This calculator uses whichever limit is tighter after your existing debts.
Why is this lower than what my bank approved?
Banks sometimes approve higher amounts based on their own risk models. This calculator is deliberately conservative and income-driven, which is closer to what is comfortable to repay rather than the maximum you could borrow.
Does it include property tax and insurance?
It reserves roughly a fifth of the housing budget for tax and insurance before sizing the loan, since those are real monthly costs. Actual amounts vary by location, so treat it as an estimate.
