House affordability calculator.
How much home your income supports — with the max price shown at several down payments.
The 28/36 rule
Lenders size a mortgage using two debt-to-income limits: the "front-end" ratio caps housing costs at about 28% of your gross monthly income, and the "back-end" ratio caps all your debt payments (housing plus car, student and credit-card minimums) at around 36%. This calculator applies both and uses whichever is more restrictive, then subtracts your estimated taxes and insurance to find the loan your income supports. Because the down payment simply adds to the price you can pay, the table shows the maximum home price at several down-payment levels. It's a planning estimate — actual approval also weighs your credit score, assets and the lender's own limits. Once you have a target price, the mortgage calculator shows the payment and the cash-to-close estimator the upfront cost.
A worked example
On a $90,000 salary — $7,500 gross a month — the front-end limit allows $2,100 for housing (28%). The back-end limit allows $2,700 for all debt (36%); if you already pay $500 a month toward a car and credit cards, that leaves $2,200 for housing. The lower of the two binds, so the housing budget is $2,100.
Subtract an estimated $450 a month for property taxes and insurance and about $1,650 remains for principal and interest. At 6.5% over 30 years that supports a loan of roughly $261,000 — which is a $290,000 home with 10% down, or about $326,000 with 20% down.
Why the rate matters more than the down payment
People tend to focus on the deposit, but the interest rate moves the affordable price harder. The down payment adds to your budget once; the rate changes how much loan each monthly dollar buys, for the whole term. A rate rise of a single percentage point can cut the supportable loan by roughly a tenth, wiping out the effect of years of extra saving.
That said, reaching 20% down does two things at once: it removes mortgage insurance from the monthly figure, which frees budget for principal and interest, and it increases the price the same loan can reach.
What the ratios do not decide
The 28/36 rule is a lender heuristic, not a law, and real underwriting is more flexible. Some loan programmes routinely approve higher back-end ratios for borrowers with strong credit or substantial reserves; others are stricter. Approval also weighs your credit score, employment history and assets left over after closing.
More importantly, the maximum a lender will approve is not the same as the amount you should borrow. The ratios use gross income and ignore tax, retirement contributions, childcare, commuting and maintenance — a rule of thumb is to budget around 1% of the home's value each year for upkeep. Borrowing to the ceiling leaves nothing for the boiler. This is a planning estimate and general education, not financial advice.