30% Rule (Affordability Standard)

What Is the 30% Rule?

The 30% rule is the most common test of housing affordability in the United States. It holds that a household should spend no more than 30% of its gross (pre-tax) income on housing costs. For renters, that means rent plus utilities. For owners, it means mortgage payments, property taxes, insurance, and utilities.

Households above the line are described as having a cost burden. Those spending more than 50% have a severe cost burden.

How It Works

The percentage-of-income standard entered federal policy as a rent formula, not as an economic finding. The Brooke Amendment to the Housing and Urban Development Act of 1969 capped public housing rents at 25% of a tenant’s income. In 1981 that cap rose to 30%, and the figure became the standard benchmark for affordability.

Today the 30% figure shows up across housing policy:

• Assisted housing rents. Federal law generally sets the basic contribution of a public housing or voucher household at the highest of 30% of monthly adjusted income, 10% of monthly gross income, or a designated welfare rent. That figure is the total tenant payment.
• Rent limits. Programs such as the Low-Income Housing Tax Credit cap rents at 30% of an income limit tied to area median income.
• Research and advocacy. Cost-burden counts and the housing wage both rest on the 30% standard.

Example

Suppose a nurse earns $72,000 a year, or $6,000 a month. Under the 30% rule, an affordable rent including utilities would be about $1,800 a month. Paying $2,400 would mean spending 40% of income on housing, which counts as cost-burdened.

Why It Matters for Workforce Housing

Workforce housing is often defined by applying the 30% rule to moderate incomes. A home is “workforce affordable” when a teacher, firefighter, or retail manager in the local labor market can rent or buy it without exceeding 30% of income. When local rents outpace those wages, even full-time workers become cost-burdened.

Criticisms and Limitations

The rule is simple, which is both its strength and its weakness. It treats a single adult and a family of five the same way, and it ignores local costs for child care, transportation, and health care. A high earner can spend 40% on housing and still live comfortably, while a low-income family at 30% may struggle. Some researchers, including a team at Harvard’s Joint Center for Housing Studies, have tested residual income measures as an alternative. These look at whether the money left after housing is enough to cover other necessities.