How Much House Can I Afford? The 28/36 Rule Explained

The 28/36 Rule

The 28/36 rule is the conservative guideline most US mortgage lenders apply to qualify borrowers for a conventional conforming loan. The rule says: no more than 28% of gross monthly income should go to total housing expense (the front-end ratio), and no more than 36% of gross monthly income should go to total debt service including housing, auto loans, student loans, credit card minimums, and any other recurring debt (the back-end ratio).

The rule is not law — it is the qualification threshold most lenders apply to loans destined for sale to Fannie Mae or Freddie Mac. The Government Sponsored Enterprises (GSEs) set the standard; lenders that originate to the GSE standard apply it. Loans that exceed 43% back-end are generally not "qualified mortgages" under the Dodd-Frank Ability-to-Repay rule (12 CFR §1026.43) and face tighter scrutiny, though Fannie Mae and Freddie Mac have historically been authorized to purchase some loans above 43% under temporary exemptions.

The rule is conservative by design. It exists to prevent the household leverage ratios that triggered the 2008 mortgage crisis, when many borrowers were carrying 50%+ back-end ratios on adjustable loans that reset upward into unaffordability.

Front-End Ratio: The 28% Ceiling

The front-end ratio, also called the housing ratio, is total monthly housing expense divided by gross monthly income. Total monthly housing expense includes:

Principal and interest on the mortgage itself
Property taxes — typically 0.5% to 2.5% of home value per year, varying by state and county
Homeowner's insurance — typically \$1,000-\$3,000 per year for a standard owner-occupied home
HOA dues, if the property is in a homeowner's association
Private mortgage insurance (PMI), if the down payment is less than 20% — see below

The combined figure is often called PITI: principal, interest, taxes, and insurance. Lenders require PITI be escrowed into the monthly payment for most conforming loans, so the borrower experiences it as a single monthly number.

Back-End Ratio: The 36% Ceiling

The back-end ratio adds all other recurring debt service on top of PITI:

Auto loan payments
Student loan payments (typically 1% of outstanding balance per month under Fannie Mae guidelines, or the actual reported payment under Freddie Mac)
Minimum credit card payments (typically the greater of 5% of balance or \$25)
Child support and alimony
Any other recurring obligation that appears on the credit report

The back-end ratio is the binding constraint for most borrowers under age 45, who typically carry auto and student debt. A high earner with no other debt can comfortably exceed 28% on the front-end if the back-end stays under 36%.

Worked Example: \$80,000 Household Income

Suppose a household earns \$80,000/year gross. Monthly gross income is \$6,667.

The 28% front-end ceiling allows: 0.28 × \$6,667 = \$1,867/month in PITI.

The 36% back-end ceiling allows: 0.36 × \$6,667 = \$2,400/month in total debt service. Subtracting \$533/month for a typical car payment and student loan leaves \$1,867/month for PITI — the same as the front-end ceiling in this case, which is why the two constraints often bind simultaneously.

Now reverse-engineer the purchase price. If property taxes run 1.2% per year and homeowner's insurance \$1,500/year, the non-mortgage portion of PITI on a \$250,000 home is roughly \$375/month. That leaves \$1,867 − \$375 = \$1,492/month for principal and interest. At a 6.75% 30-year fixed rate, \$1,492/month supports a loan of roughly \$230,000. With a 10% down payment on a \$255,000 purchase price, the loan amount is \$229,500 — right at the affordability ceiling.

Bump household income to \$120,000 and the math scales linearly: \$2,800/month for PITI, supporting roughly a \$400,000 purchase price with the same assumptions. The rule scales with income; the ratios stay constant.

Costs Beyond PITI That Buyers Forget

Closing costs. Typically 2-5% of purchase price, paid at closing. On a \$250,000 home, that is \$5,000-\$12,500 in addition to the down payment.
Property maintenance. The 1% rule of thumb says to budget 1% of home value per year for repairs and capital expenditures. On a \$250,000 home, that is \$2,500/year or roughly \$210/month.
Utility increases. Moving from an apartment to a 2,000-sqft home typically raises electricity, gas, water, and internet costs by \$200-\$500/month.
Move-in costs. Furniture, window treatments, lawn equipment, paint, and minor repairs in the first 90 days can easily run \$5,000-\$15,000.

A borrower at the 28/36 ceiling has no financial margin for these. Prudent buyers typically target a 25% front-end ratio to leave breathing room for the unbudgeted expenses that always accompany homeownership.

PMI and the Homeowners Protection Act

If your down payment is less than 20% of the purchase price, the lender will require private mortgage insurance (PMI), which typically costs 0.3% to 1.5% of the original loan amount per year. On a \$230,000 loan with a 0.5% PMI rate, that is \$1,150/year or about \$96/month — money that buys no equity and disappears at cancellation.

The Homeowners Protection Act of 1998 (12 U.S.C. §4901) gives borrowers three cancellation pathways:

Borrower-requested cancellation at 80% loan-to-value (LTV), provided the borrower has a good payment history and the property has not declined in value.
Automatic termination at 78% of the original LTV, regardless of payment history (with limited exceptions).
Midpoint termination: PMI must terminate at the midpoint of the loan's amortization schedule, even if LTV has not been reached, if the borrower is current on payments.

The HPA does not apply to FHA loans, which carry their own mortgage insurance premium (MIP) structures under HUD rules — typically for the life of the loan if the down payment is less than 10%. FHA borrowers cannot cancel MIP at 78% LTV the way conventional borrowers can cancel PMI.

Stress-Testing Your Budget

The 28/36 rule assumes today's income and today's rates. Both can change. Before signing, model three stress scenarios:

Rate shock. If you take an adjustable-rate mortgage, model the payment at the rate ceiling. Can you still afford PITI at the maximum contract rate?
Income loss. If one earner in a two-income household loses their job, can the other cover PITI plus minimum debt service? Most planners recommend 6 months of expenses in an emergency fund before buying.
Property tax reassessment. Many states reassess on sale; the seller's tax bill may not be the buyer's. A \$4,000/year reassessment adds \$333/month to PITI.

Condo, HOA, and Special Assessment Considerations

Condominiums and properties in homeowner's associations carry monthly HOA dues that must be added to PITI for affordability calculation. HOA dues vary widely: \$100-\$300/month is typical for a basic condominium with no amenities; \$400-\$800/month is common for buildings with pools, gyms, and 24-hour staff; and \$1,500+/month appears in luxury high-rises. The 28% front-end ratio includes HOA dues alongside principal, interest, taxes, and insurance.

Buyers should also budget for special assessments — one-time charges levied by the HOA for major capital expenditures such as roof replacement, elevator modernization, or structural repairs. A 2023 reserve study by the Foundation for Community Association Research found that approximately 30% of community associations in the United States are underfunded for projected capital reserves, meaning future special assessments are likely. Before purchasing a condo, review the HOA's reserve study and the minutes of the last 24 months of board meetings for evidence of deferred maintenance or pending assessments.

The Federal Housing Administration requires condominium projects to be on its approved list (or pass a single-unit approval review) before an FHA-insured loan can be originated. Fannie Mae and Freddie Mac maintain similar project review requirements. These approvals add lead time and may disqualify buildings with high investor concentration, high delinquency rates on HOA dues, or insufficient reserves.

Conclusion

The 28/36 rule is a starting point, not a finish line. It tells you what a conforming loan underwriter will approve; it does not tell you what you can comfortably live with. The borrowers who sleep well at night are typically those at a 25/32 ratio with a six-month cash reserve. The borrowers who lose houses in the next recession are typically those at a 30/40 ratio with nothing in reserve and a rate reset looming.

Run your own numbers with our Mortgage Calculator and cross-check your back-end ratio against your full debt service.

This article is for educational purposes only and does not constitute financial or lending advice. Mortgage qualification varies by lender, loan product, and borrower profile. See our disclaimer for full terms. Written by the HT99 Tools Editorial Team.