How Much House Can I Afford? The 28/36 Rule, DTI Math, and Down Payment Effects

When buyers ask how much house they can afford, they usually picture a price — $450,000, say. Lenders, by contrast, think in payments relative to income. The bridge between the two is the monthly housing cost: principal and interest on the loan plus property tax, homeowner’s insurance, private mortgage insurance where applicable, and HOA dues. Two identical prices can produce very different housing costs once local tax rates, insurance zones, and association fees enter the picture, which is why ratio-based budgeting starts from income and works toward price rather than the other way around.

The Consumer Financial Protection Bureau (CFPB) frames affordability through its Ability-to-Repay framework: lenders must make a reasonable, good-faith determination that a borrower can repay, weighing income, assets, employment, credit history, and debt obligations. Under the Qualified Mortgage approach that grew out of that framework, a total debt-to-income ratio at or below 43 percent became a widely cited threshold. Planning guides commonly pair that ceiling with a softer housing-only target near 28 percent of gross income — the number that keeps the payment comfortable rather than merely approvable. Start your research at consumerfinance.gov/consumer-tools/mortgages, where the CFPB publishes home-buying toolkits and sample disclosure forms.

Gross income — pay before taxes and deductions — is the denominator in every ratio here, because that is the convention lenders and the CFPB use. Net take-home pay matters for your lived budget, and you should sanity-check any ratio result against it, but do not mix the two when comparing your numbers to guideline thresholds. If your income includes overtime, bonuses, commissions, or self-employment earnings, lenders typically average it over one to two years of documentation rather than accepting a single strong month, so use a conservative, documented figure in your own math and let your lender confirm the qualifying amount.

The 28/36 rule has two halves. The front-end ratio caps housing cost — the full PITI-plus bundle of principal, interest, property tax, homeowner’s insurance, mortgage insurance, and HOA — at roughly 28 percent of gross monthly income. The back-end ratio caps all recurring minimum debts, housing included, at roughly 36 percent. Car payments, student loan payments, and credit-card minimums are the usual back-end additions; utilities, groceries, subscriptions, and income taxes are not counted in either ratio, which is one reason the guideline payment can still feel tight if the rest of your budget is heavy.

These percentages are conventions, not statutes. Different loan programs publish different ceilings: conventional conforming guidance has historically discussed total DTI bands in the mid-30s to mid-40s percent range depending on compensating factors, FHA programs may allow higher back-end ratios with strong reserves or residual income, and VA underwriting leans on residual income alongside ratios. Freddie Mac’s home-buying research similarly describes affordability in terms of payment share of income rather than a single universal cutoff. Treat 28/36 as the conservative planning default and ask your lender which thresholds your program actually enforces — the answer determines whether the guideline or the program rule binds first.

The practical way to use the rule is as a two-gate test. First, multiply gross monthly income by 0.28 to get the guideline housing budget. Second, multiply it by 0.36, subtract current non-housing minimum debts, and treat the remainder as the debt-constrained housing budget. Your planning payment is the smaller of the two. When non-housing debts are light, the 28 percent gate binds; when student or auto debt is heavy, the 36 percent gate binds and paying down those balances can raise your housing budget faster than a raise would.

The formulas are simple division. Front-end DTI equals proposed monthly housing cost divided by gross monthly income. Back-end DTI equals the sum of housing cost plus all recurring monthly minimum debts, divided by the same income. Walk through a household earning $90,000 per year, or $7,500 per month gross. The 28 percent gate gives $7,500 × 0.28 = $2,100 per month for housing. The 36 percent gate gives $7,500 × 0.36 = $2,700 for all debts. If the household carries a $380 car payment, $320 in student loans, and $100 in card minimums — $800 total — the debt-constrained housing budget is $2,700 − $800 = $1,900. The smaller gate wins, so the planning payment is about $1,900 per month including tax, insurance, and HOA.

Now change one variable: the same household pays off the car, dropping non-housing debt to $420. The debt-constrained budget becomes $2,700 − $420 = $2,280, and the 28 percent gate at $2,100 binds instead. The planning payment rises from $1,900 to $2,100 without any change in income — a $200 monthly swing from a single paid-off loan. This is why advisors often suggest modeling affordability before and after expected debt payoffs rather than treating current minimums as fixed. Test both states in our affordability calculator, then translate each payment into a price with the mortgage calculator by entering local tax and insurance figures.

A second example shows how the back-end ceiling interacts with program limits. Take a household earning $140,000 per year ($11,667 monthly). The 28 percent housing target is about $3,267; the 36 percent all-debt guideline is about $4,200. With $1,100 of non-housing minimums, the implied housing budget is $4,200 − $1,100 = $3,100 — slightly below the 28 percent figure, so debt is the binding constraint again. But some loan programs may permit total DTI into the low-to-mid-40s percent range with compensating strengths such as large reserves or a strong credit profile. At a hypothetical 43 percent program ceiling the all-debt allowance would be about $5,017, leaving roughly $3,917 for housing after the same $1,100 — well above the 28 percent comfort target. The gap between $3,100 and $3,917 is the difference between comfortable and maximum: a lender might approve the higher payment while your budget prefers the lower one. Always confirm which ceiling your lender applies and choose the payment you can sustain through income dips, not just the one you can document today.

Down payment enters affordability through three channels at once: it reduces the amount financed, it can eliminate or shrink mortgage insurance, and it affects the rate and program choices a lender offers. On conventional loans, reaching 20 percent equity generally avoids private mortgage insurance entirely; below that, PMI typically adds a monthly charge that varies with credit score and loan-to-value until you reach 20 percent equity with cancellation rights, or automatic termination near 22 percent for qualifying loans under the Homeowners Protection Act. FHA loans follow HUD rules instead: an upfront mortgage insurance premium plus an annual MIP paid monthly, which on many small-down-payment loans lasts for the life of the loan.

Ratios treat every dollar of housing cost equally, but the composition matters for risk. Property tax is set by local jurisdictions and can be reassessed after purchase — sometimes sharply when a sale resets assessed value. Homeowner’s insurance reflects rebuild cost, deductible, and regional perils; in wildfire, hurricane, and flood-exposed markets, premiums and separate wind or flood policies can add hundreds per month beyond mainland expectations. HOA dues are set by associations and can rise through regular increases or special assessments for roofs, siding, or amenities. None of these amortize or shrink with extra principal payments, so a payment that looks comfortable on principal and interest alone can breach the 28 percent target once the full bundle lands.

Upkeep sits outside DTI entirely yet determines whether the payment is sustainable. A widely cited planning range puts routine maintenance around 1 percent of home value per year, with older homes, pools, wells, and septic systems pushing higher — confirm with a local inspector rather than treating any rule of thumb as a quote. Add utilities, which landlords sometimes cover but owners always pay, and the true cost of occupying the house can run several hundred dollars above the lender’s housing figure. Build these into a parallel take-home budget: if the ratio-approved payment plus maintenance and utilities exceeds roughly a third of take-home pay, consider a lower price even when the gross-income math says yes.

Location tilts every input at once. A lower price in a high-tax district can cost more monthly than a higher price in a low-tax one; a condo with a $450 HOA can lose to a slightly pricier single-family home with none. Compare listings by total monthly carrying cost — modeled in the mortgage comparison calculator with local tax and insurance per property — rather than by sticker price. Adjustable-rate structures add another layer: our ARM calculator shows how post-fixed-period adjustments could move a payment that starts inside your band.

A calculator narrows the band; pre-approval tests it. Expect the lender to verify income with pay stubs, W-2s, and tax returns, source large deposits in bank statements, pull credit from the major bureaus, and apply program overlays your estimate cannot see — employment history rules, self-employment averaging, rental-income haircuts, and condo project approvals among them. Bring the output of this guide as a starting position, not a verdict: the payment you want and the amount the lender approves are two inputs to one decision, and the right purchase price is usually at or below the smaller of the two.

Compare at least two or three Loan Estimates line by line — rate, points, lender credits, origination charges, and cash to close — because the same price can carry materially different costs across lenders (our points-vs-rate guide shows how upfront points trade against monthly payment). If refinancing later is part of your plan, sanity-check the long-run math in the refinance calculator, and if biweekly-style acceleration appeals, the biweekly mortgage calculator models one extra payment per year. Government-backed paths have their own calculators when relevant: FHA loan calculator for low-down-payment MIP math and VA loan calculator for eligible borrowers comparing funding fees against PMI. Start every scenario from the loan tools center.