There is no income number that qualifies you for a mortgage. Lenders do not ask whether you earn enough; they ask what fraction of your income the payment would consume, and whether the rest of your obligations leave room for it.
That framing changes the question from "can I afford a $500,000 house" to "what payment fits inside my ratios," which is a question with an actual answer.
The two ratios
The front-end ratio is your total monthly housing cost divided by gross monthly income. The conventional guideline caps it at 28%.
The back-end ratio is all your monthly debt payments — housing plus everything else — divided by the same gross income. The guideline caps it at 36%.
Both use gross income, before taxes and deductions. This is the source of most of the gap between what a lender approves and what a household can comfortably carry, because the borrower experiences the payment out of net pay.
What goes in the housing number
The housing cost is PITI: principal, interest, taxes, and insurance. Add mortgage insurance if the down payment is under 20%, and HOA dues if the property has them.
Property taxes alone can be substantial. The national average effective rate is roughly 0.99% of home value per year, but state-level rates run from around 0.3% to over 2.2%. On a $400,000 home, that spread is $100 versus $733 a month — enough to change which house you qualify for entirely.
Homeowners insurance varies similarly by region and has risen sharply in some markets. Estimating it at a national average is one of the ways affordability calculators quietly mislead.
A full worked example
Take a household with $100,000 of gross annual income, or $8,333 a month. They have a $450 car payment and $200 in student loan payments.
Front-end limit: 28% of $8,333 is $2,333 for total housing costs.
Back-end limit: 36% of $8,333 is $3,000 for all debt. Subtracting the $650 of existing payments leaves $2,350 available for housing.
The binding constraint is the lower of the two, so $2,333 a month is the housing budget.
Now decompose it. In a market with a 1.1% effective property tax rate on a $400,000 home, taxes are about $367 a month. Insurance might be $150. That leaves roughly $1,816 for principal and interest.
At 6.58%, $1,816 a month supports a loan of roughly $285,000. Add a 20% down payment and the affordable purchase price is around $356,000 — not the $400,000 the household might have assumed from a rule of thumb about multiples of income.
What the existing debt is really costing
That $450 car payment is worth examining, because within the back-end ratio it directly displaces borrowing capacity.
Removing it would free $450 of monthly room, and at 6.58% over thirty years, $450 a month supports roughly $70,000 of additional mortgage. A car loan with two years left is, in mortgage-qualification terms, a $70,000 reduction in what you can buy.
This is why paying down or paying off installment debt before applying often does more for approval than saving a larger down payment. It is also why taking on a new car loan while under contract is one of the reliable ways to lose a mortgage approval before closing.
Where the guideline bends
Automated underwriting from Fannie Mae and Freddie Mac routinely approves back-end ratios above 36% when there are compensating factors: a high credit score, substantial cash reserves after closing, a large down payment, or a documented history of paying similar housing costs.
FHA loans, which are aimed at borrowers with thinner credit or smaller down payments, permit higher ratios in many cases as well.
Approval and affordability are not the same test, though. A household approved at a 45% back-end ratio on gross income may be committing well over half of take-home pay to debt, leaving nothing for retirement contributions, the emergency fund the house will eventually require, or the ordinary cost of living somewhere.
A more honest personal test
Run the ratios on net income rather than gross and see how they look. Then add the costs a lender does not count and a homeowner definitely pays: maintenance at roughly 1% of home value a year, utilities that are typically higher than in a rental, and the appliance that fails in month four.
A practical dry run: put the difference between your current housing cost and the proposed payment into savings every month for three or four months before you buy. If that is comfortable, the number is real. If it is not, you have learned it for the price of some extra savings rather than at closing.