How much house can I afford? The 28/36 rule, and why it lies

Walk into any mortgage broker and you’ll get a pre-approval letter for a number bigger than you can actually live with. That gap — between what lenders consider “qualified” and what your budget can sustain — is where most first-time buyer regret lives. This guide explains the two rules of thumb every US lender uses (28% and 36%), what they actually measure, and the four cost categories the rules ignore.

The 28/36 rule, decoded

Two ratios. Both come from the Consumer Financial Protection Bureau’s Qualified Mortgage rule and its predecessors in HUD’s underwriting guidelines.

• Front-end ratio (28%): housing costs ÷ gross monthly income. Housing here is PITI: principal, interest, property taxes, homeowner’s insurance. Up to 28% is considered conservative.
• Back-end ratio (36%): all debt service ÷ gross monthly income. Includes the PITI above plus car loans, student loans, credit card minimums, alimony, child support. Up to 36% is conservative; up to 43% is allowable under standard QM rules, and FHA goes to 50% under specific circumstances.

Note the denominator: grossmonthly income, not take-home. For a household with a 30% effective tax burden (federal + state + payroll), the 28% front-end ratio is really 40% of net income. That’s before you’ve paid for groceries, retirement, daycare, or transport.

What lenders won’t include in PITI

The rule of thumb covers four things. Actual home ownership has at least four more, all of which are predictable long-term costs:

• Maintenance and repair:the standard forecast is 1-3% of the home’s value per year. On a $500,000 house, that’s $5,000-15,000 annually. Roof, HVAC, water heater, appliances, paint, landscaping all wear out on their own schedule.
• Utilities: heating, cooling, water, electricity, internet, garbage. $250-600/month depending on climate and house size.
• HOA fees:$0 in a stand-alone house, $200-1000+/month in condos, townhouses, and master-planned communities. Often not capped — they rise with the association’s reserve deficits.
• Furnishings & one-time setup: moving, window treatments, appliances the seller took, lawn equipment, tools. Plan 1-5% of the purchase price the first year alone.

A worked example: what the rule says vs what fits

Household: $180,000 gross income, $60,000 down payment, $400 student loan, $300 car loan. 7% mortgage rate, 30-year fixed, 1.1% effective property tax, $1,500/year insurance.

What lenders qualify: 36% back-end ratio on $180k gross = $5,400/month total debt. Subtract $700 of existing loans → $4,700 available for PITI. At 7% / 30y, that supports a mortgage payment that comes from a roughly $750,000 home (with the $60k down).

What the home actually costs:

$7,053 ÷ $15,000 gross = 47%. That’s comfortably past the comfort line. Take-home (~$10,500 after tax) leaves $3,450 a month for everything else: groceries, retirement, daycare, transport, savings, fun. Doable, but tight — and one HVAC failure away from the emergency fund.

A more honest rule of thumb

The financial-planner version: target 25% of net income for all housing costs includingmaintenance and utilities. For the household above ($10,500 net), that’s $2,625 — corresponding to a home around $320,000, less than half of what the lender will approve.

That’s probably too strict if you have stable income, emergency savings, and modest other expenses. But the gap between $750k (the lender ceiling) and $320k (the 25%-of-net floor) is the range you actually have to think about.

Stress tests worth running

1. Can you cover a 20% income drop for 6 months? If one earner loses their job, does the mortgage payment plus essentials fit on the remaining household income?
2. What happens at rate reset? ARM borrowers should run the worst-case rate after the fixed period. Even fixed-rate borrowers should think about it for potential future refinancing.
3. What’s the 15-year payment? Run the numbers — if the 15-year mortgage payment is unreachable, the 30-year is probably tighter than it feels. See our 15- vs 30-year comparison.
4. HOA + tax escalators? Both have outrun inflation in many US metros. Build in 5-10% annual increases when projecting 5+ years out.

The pragmatic bottom line

Use a mortgage calculator with the lender’s pre-approval number to find the actual monthly payment, then add 1.5-2% of home value annually for maintenance + utilities. If the resulting all-in housing cost exceeds 30% of your take-home pay, the house the bank says you can afford is bigger than the house your budget can absorb.

Sources: CFPB’s 2014 Qualified Mortgage rule (12 CFR 1026.43), HUD Single-Family Housing Policy Handbook 4000.1, Joint Center for Housing Studies State of the Nation’s Housing 2024.