If you've ever wondered why a lender pre-approved you for a smaller loan than you expected — or a much bigger one — the answer almost always traces back to the 28/36 rule. It's the framework underwriters use to decide whether your debt-to-income ratios fit conventional lending standards. Understanding it lets you back-calculate the price range you'll actually be approved for, before you ever talk to a loan officer.
What the two numbers mean
- 28% — front-end ratio. Your monthly housing expense (PITI + HOA) should not exceed 28% of your gross monthly income.
- 36% — back-end ratio. Your total monthly debt (housing + car loans + student loans + credit card minimums + child support) should not exceed 36% of gross monthly income.
"Gross" means before tax. Both rules apply simultaneously — the lower of the two caps you. Some lenders stretch the back-end to 43% or 45% for strong borrowers, but 36% is the textbook target and the safest budget rule for the borrower.
What "housing expense" actually includes
Underwriters don't just look at your principal-and-interest payment. The full PITI includes:
- Principal
- Interest
- Taxes (property tax, escrowed monthly)
- Insurance (homeowners + PMI if down payment < 20%)
Plus HOA fees if applicable. A buyer in a $250 HOA condo gets less mortgage approved than one buying a similarly priced single-family home — even with identical income and credit.
Worked example: $9,000/month gross income
Front-end cap: $9,000 × 0.28 = $2,520/month for housing
Back-end cap (assuming $600/month in other debts): $9,000 × 0.36 − $600 = $2,640/month for housing
The front-end is the binding constraint here. Working backward from $2,520/month in housing:
- Property tax (~1.2% annually): $400/month
- Insurance: $120/month
- Available for P&I: $2,000/month
- At 6.75% over 30 years, $2,000 supports a loan of ~$308,000
- With 10% down: max purchase price ~$342,000
That is the price ceiling a strict 28% front-end gives a $108K-income buyer in a 1.2% property tax county at today's rates. Drop the rate to 5% and the same income supports ~$365K. Move to a 2% property tax state and it drops to ~$310K.
Why your pre-approval might be higher
Most lenders will go above 28%/36% if your overall financial profile is strong:
- Credit score 760+: stretches both ratios slightly
- Significant cash reserves (6+ months of payments in savings)
- FHA loans allow back-end ratios up to 43% and sometimes 50%
- Conforming conventional loans frequently approve at 45%
A pre-approval at 45% back-end is not the same as 45% being affordable. It's the maximum the lender will lend, not the maximum a sane budget can absorb. Most financial planners suggest staying under the textbook 36%.
The hidden costs the rule doesn't capture
The 28/36 framework was designed when home maintenance, utilities, and commuting were smaller line items than today. A more realistic budget adds:
- Maintenance: 1%–2% of home value per year
- Utilities: $250–$450/month for a typical single-family home
- Commuting: if the affordable house is 30 miles further out, factor in $300–$600/month in additional gas, tolls, and vehicle wear
Try the calculator
Our house affordability calculator applies the 28/36 rule (and lets you override the percentages), accounts for property tax and HOA, and gives you the maximum loan and home price in seconds.