- A lender’s pre-approval is an underwriting estimate, not a household comfort target. Build the purchase limit from your own cash flow.
- Ratio benchmarks can be useful for orientation, but underwriting rules and a sustainable take-home budget are not the same test.
- Principal and interest are only part of ownership cost; include taxes, insurance, association charges, maintenance and utilities.
- Buy for the monthly payment you can sustain, not the purchase price you can reach.
Ask a lender how much house you can afford and you'll receive a number that answers a different question: how much they're willing to lend before your default risk becomes uncomfortable for them. Their ceiling and your comfortable budget are separated by everything a mortgage payment doesn't include — and by the difference between qualifying on paper and living well in practice. Here's how to compute your own number before anyone shows you houses.
Why the pre-approval overshoots
Lenders qualify you on gross income and count only debts that appear on your credit report. Your actual life runs on take-home pay and includes childcare, retirement contributions, groceries, travel and everything else that never touches a credit bureau. A household grossing $140,000 might be approved for a payment near $3,900 — while their after-tax, after-401(k), after-daycare reality comfortably supports $2,800. Both numbers are “correct.” Only one of them lets you keep saving.
The 28/36 rule — a starting guardrail
The traditional standard: housing costs (payment, taxes, insurance) below 28% of gross monthly income, and total debt payments including the house below 36%. On $140,000 gross ($11,667/month), that's a housing ceiling of about $3,270 and a total-debt ceiling of $4,200. Modern loans often approve well above these ratios — FHA can stretch past 50% total — but “can be approved” and “should sign” are different sentences. Treat 28/36 as the outer boundary and build your real number from net income.
The costs the mortgage calculator hides
The principal-and-interest figure everyone shops with is only part of the bill:
| Cost | Typical range |
|---|---|
| Property taxes | 0.5–2.5% of home value per year, varies enormously by state and county |
| Homeowners insurance | $1,200–$3,000+/yr; far more in disaster-prone regions |
| PMI (down payment under 20%) | 0.3–1.5% of loan per year until ~20% equity |
| HOA/condo fees | $0–$600+/month where applicable |
| Maintenance & repairs | Budget 1–2% of home value annually — lumpy but inevitable |
| Utilities step-up | Houses cost more to heat, cool and water than apartments |
Stack these and the true monthly cost of ownership typically runs 25–50% above the principal-and-interest number. A “$2,400 mortgage” is often a $3,300 house.
Compute your number in five steps
- Start from monthly take-home pay — after taxes and after retirement contributions you refuse to pause.
- Subtract real non-housing spending: debts, food, transport, childcare, healthcare, subscriptions, honest fun budget.
- Subtract continued saving — emergency fund maintenance and goals beyond the house.
- What remains is your all-in housing budget. Multiply by ~0.75 to get the principal-and-interest portion; that's the number to put into mortgage calculators.
- Convert to price using current rates and your down payment. Keep an emergency fund after closing — a house with no cushion is a stress machine.
Adjustments worth making
- Variable income: compute from your conservative-year income, not your best year.
- Planning kids or a career change: qualify the future budget, not the current one.
- High-property-tax states: taxes can rival the mortgage itself over time — check the actual parcel's history, not the county average.
- First home: budget a furniture-and-fixes fund for year one; nearly everyone underestimates it.
Reader questions, answered
Is 20% down still necessary?
No — conventional loans go to 3% down and FHA to 3.5%. Under 20% you'll pay PMI until you reach ~20% equity, which adds cost but can be rational when rents are high and prices rising. It's a trade-off, not a rule.
Should I stretch now since my income will grow?
Careful. Stretching assumes the raise arrives, no shocks intervene, and rates/taxes/insurance stay tame. The strained years arrive first and compound. Buying within today's means and upgrading later is the lower-regret path for most.
Renting vs buying — how do I compare honestly?
Compare rent against the full ownership cost (payment, taxes, insurance, maintenance, HOA) minus principal paydown and expected appreciation, and weigh how long you'll stay — under five years, transaction costs often make renting win outright.
Do online affordability calculators account for all this?
Most don't — they typically show principal and interest, sometimes taxes and insurance, and almost never maintenance, PMI details or your real take-home budget. Use them for the P&I conversion in step 4, not for the decision itself.
Sources and methodology
We use primary regulator guidance and public product documentation. Rates and product terms change, so verify current details with the provider before acting.