Housing Cost Burden: The 30% Rule and What HUD's Definition Misses

The federal definition is simple: if a household spends more than 30% of its gross income on housing — rent or mortgage plus utilities and insurance — it is 'cost-burdened.' Above 50% it is 'severely cost-burdened.' Roughly one in three U.S. households (about 40 million) crosses the first threshold; about 17% cross the second.

Census table B25070 (gross rent as percentage of household income) lets you see this directly for every ZIP code in America. The variation is enormous — under 15% of households are cost-burdened in parts of rural Iowa; over 60% in coastal California neighborhoods.

Where the 30% rule came from

The threshold dates to the 1969 Brooke Amendment, which capped public-housing rents at 25% of tenant income. Congress raised it to 30% in 1981. There is no economic theorem behind the number — it is an administrative cutoff that, after four decades of use, has become the default measure of housing affordability nationwide.

Critics argue the rule is too rigid. A household earning $250,000 spending 35% on housing has different financial slack than one earning $40,000 spending 28%. The dollar 'residual income' left after housing matters more than the percentage for low-income households. Several states (Massachusetts, Vermont) supplement the 30% rule with residual income tests for their own affordability programs.

Where cost burden concentrates

The geography of cost burden is the geography of expensive coastal metros plus tourism economies. Florida tops the list of cost-burdened states largely because of low wages relative to coastal housing, not because Miami is more expensive than San Francisco in absolute terms.

California, New York, and New Jersey have high cost burden among renters. Florida and Hawaii lead among all households. The lowest-burden states are concentrated in the Midwest and northern Plains.

• Highest renter cost burden: Florida (54%), California (53%), Hawaii (52%)
• Lowest renter cost burden: South Dakota (38%), Wyoming (39%), North Dakota (39%)
• National average: 49% of renters and 23% of owners are cost-burdened

Why owners and renters diverge

Homeowners with fixed-rate mortgages locked in years ago face a very different cost trajectory than renters whose contracts reprice annually. As home prices rose 50% from 2019 to 2023, owners with pre-2020 mortgages saw their housing costs rise only with inflation. Renters absorbed the full market move.

This is why national homeowner cost burden actually fell during the 2020–2023 boom while renter cost burden spiked — and why the rent-vs-buy decision is so much more consequential today than it was a decade ago.