Why the 28/36 Rule Fails Most Homebuyers in 2025

The 28/36 rule tells you to spend no more than 28% of gross income on housing and no more than 36% on total debt. It is printed on every real-estate agent’s affordability handout and built into every lender’s first-pass screen. It is also the wrong rule for most first-time buyers in 2025, because it was designed for a household that had none of the things a 2025 household has: $70,000 of student loans, $250/month in HOA dues, and a homeowner’s insurance bill that has doubled in five years.

What the 28/36 rule actually covers (and doesn’t)

The 28% housing portion is usually defined as PITI: principal, interest, property tax, and insurance. In high-HOA markets like South Florida condos, Arizona master-planned communities, and California attached housing, HOA dues frequently run $400-800 per month. Those are fixed housing costs that feel like a mortgage but sit outside the 28% test unless you remember to add them. The CFPB’s loan options guide lays out what PITI means, but not how to adjust for these modern line items.

The DTI math lenders actually run

Forget 28/36. What matters at underwriting is the back-end debt-to-income ratio: the sum of your future PITI payment plus every other monthly debt (student loans, auto loans, credit card minimums, alimony), divided by your gross monthly income. Conventional loans sold to Fannie Mae or Freddie Mac generally cap this at 43%, the threshold set by the CFPB Qualified Mortgage rule. FHA loans stretch higher, often to 50% with strong compensating factors like solid credit, six months of cash reserves, or a long job tenure.

Put numbers on it. A household earning $10,000/month gross, with $600 in student loans, $450 in car payments, and $100 in credit card minimums, can carry up to $3,150 in PITI before hitting the 43% cap. Subtract $400 for property tax and $200 for insurance, and the principal-and-interest budget is about $2,550. At current 30-year rates near 7%, that supports roughly a $385,000 loan, materially less than the 28%-of-income path would imply.

Property tax and insurance: the regional multiplier

Affordability comparisons across cities are useless without explicit tax and insurance math. Pull the effective property tax rate from Census American Community Survey or your county assessor. At a 2.2% rate in Illinois, a $450,000 home adds $825 per month in property tax. At 0.3% in Hawaii, the same price tag adds $113. That $700/month gap, capitalized at a 7% mortgage rate, is worth about $105,000 of principal, enough to shift which house you qualify for by a full tier.

Insurance has compounded the problem since 2022. The Insurance Information Institute reports that the national average homeowners premium has risen roughly 33% from 2020 to 2024, with Florida, Louisiana, and California carrying the steepest increases. Underwriting escrow estimates often undercount the premium on a newly purchased home, leaving the first escrow shortage notice to arrive twelve months later.

A better personal rule

Instead of 28% of gross, stress-test your target payment at 28% of net take-home income, inclusive of HOA and the realistic insurance premium. Then re-test at a rate 1.5 percentage points higher than today’s. If you can still make the payment at that rate, you have a real affordability cushion. If not, the house you are buying is affordable only as long as nothing moves, your job, rates, or the insurance market, which is rarely a safe assumption over a thirty-year term.

Run the specific numbers with our mortgage affordability calculator, which applies both the 28/36 and QM-rule 43% DTI checks, and the mortgage payment calculator for the PITI breakdown. For the tax side, pair the result with your city’s numbers from our federal income tax calculator to figure out what you actually bring home before the mortgage touches it.