Price Alone Doesn't Measure Affordability
A $350,000 house in Peoria, Illinois, where median household income is $55,000, is far less affordable than a $550,000 house in San Jose, California, where median household income is $130,000. Raw prices mislead; affordability requires relating price to income.
Housing affordability indexes exist to make this comparison systematic. Understanding them at the ZIP code level helps renters, buyers, policymakers, and investors evaluate housing markets with more nuance than headline price data allows. Compare any two ZIP codes on housing cost and income data.
The Standard Affordability Threshold: The 30% Rule
The most widely used affordability benchmark is the HUD "30% rule": housing is considered affordable when it costs no more than 30% of gross household income. Households spending more than 30% on housing are "cost-burdened"; those spending more than 50% are "severely cost-burdened."
By this measure, approximately 30% of all American households are cost-burdened — but the rate varies dramatically by ZIP code, from under 15% in affordable Midwest markets to over 50% in coastal California and Hawaii ZIPs.
The National Association of Realtors Housing Affordability Index
NAR's Housing Affordability Index (HAI) measures whether a median-income family can qualify for a conventional mortgage on a median-priced home in a given area. A score of 100 means the median family has exactly enough income to qualify; scores above 100 indicate more affordability (income exceeds minimum qualification), scores below 100 indicate less.
NAR publishes HAI at the metro and national level; similar methodologies are applied by state housing finance agencies at the county and sometimes ZIP code level.
Formula: HAI = (Median Family Income) ÷ (Qualifying Income) × 100
Where Qualifying Income = the income needed to make the monthly payment on a median-priced home at current mortgage rates, using a 20% down payment and 28% income ratio.
2026 Housing Affordability by ZIP Type
| ZIP Archetype | Typical HAI Score | Monthly Payment as % of Income |
|---|---|---|
| Rural Midwest (e.g., 61701 Bloomington, IL) | 175–220 | 13–17% |
| Small metro Midwest (e.g., 43215 Columbus, OH) | 130–170 | 17–22% |
| Sun Belt growth suburb (e.g., 78660 Pflugerville, TX) | 90–120 | 24–30% |
| Major metro suburb (e.g., 22030 Fairfax, VA) | 75–100 | 28–35% |
| Urban core, high cost (e.g., 02139 Cambridge, MA) | 45–70 | 38–50% |
| Coastal California (e.g., 94027 Atherton, CA) | 15–35 | 60–90% |
The Rent Affordability Crisis in Specific ZIP Codes
The homeownership affordability calculation above excludes renters, who face their own affordability crisis. Rent-to-income ratios in 2025–2026 show severe burden in many urban ZIP codes:
- Miami 33101: Median rent consumes approximately 58% of median household income — among the most extreme in the nation
- Los Angeles 90028 (Hollywood): ~52% rent-to-income ratio
- New York 10025 (Upper West Side): ~48%
- Boston 02139 (Cambridgeport): ~46%
- San Francisco 94110 (Mission): ~45%
Compare this to historically affordable markets like Columbus 43207 (16% rent-to-income) or Oklahoma City 73102 (19%), where the same income buys vastly more housing.
What Drives ZIP Code Affordability Differences
- Supply constraints: ZIPs with restrictive zoning and low construction rates see prices bid up as demand exceeds limited supply
- Employment premium: High-paying job clusters create bidding competitions for nearby housing
- Geographic constraints: Water bodies, mountains, and other physical barriers limit buildable land in coastal and mountain ZIPs
- Amenity premiums: Walkability, school quality, and climate drive willingness-to-pay above income-predicted levels
- Investor demand: In some ZIPs, investor and short-term rental demand (Airbnb) competes with primary residence buyers, driving up prices and reducing supply for long-term residents
Housing + Transportation Affordability
The Center for Neighborhood Technology (CNT) argues that the standard 30% housing cost threshold misses transportation costs — households in car-dependent suburban or exurban ZIP codes spend more on transportation (often $10,000–$15,000 per year per vehicle) that partially offsets their lower housing costs. CNT's H+T Affordability Index considers housing and transportation together:
- Affordable is defined as combined H+T costs ≤ 45% of income
- Transit-rich, walkable urban ZIP codes often look more affordable on this measure than their raw housing costs suggest
- Car-dependent outer suburbs look less affordable when transportation costs are included
Using Affordability Data in Your Research
- Use our ZIP code lookup to find median household income and median rent/home value for any ZIP
- Calculate your personal rent-to-income ratio: (monthly rent or mortgage) ÷ (monthly gross income) × 100. Above 30% = cost-burdened.
- Use the comparison tool to find ZIPs where your income provides more purchasing power
- Factor in transportation costs: if you're moving to a less walkable ZIP, add an estimated $800–1,200/month per vehicle to your cost comparison