Our Methodology
ZIP codes drive a huge share of US life decisions — home buying, school choice, insurance pricing. You deserve to know exactly where our ZIP-level numbers come from, and what they cannot tell you about your specific address.
Primary source: US Census Bureau ACS
Every demographic, income, housing, and education figure on ZipPeek is anchored in the US Census Bureau American Community Survey (ACS). The ACS samples roughly 3.5 million US households per year and publishes 1-year and 5-year rolling estimates by geography. For ZIP-level data, we use the 5-year ACS estimates.
ZCTA vs USPS ZIP code
A subtle but important point: the Census Bureau does not publish data by USPS ZIP code directly. Instead it publishes by ZIP Code Tabulation Areas (ZCTAs), statistical geographies the Census builds to approximate USPS ZIP service areas:
- USPS ZIP codes are delivery routes, not geographic polygons.
- ZCTAs are stable polygons designed for census comparability.
- PO box ZIPs and special-use ZIPs don't have ZCTAs.
- For most residential ZIPs, ZCTA = ZIP. For edge cases see the HUD-USPS crosswalk.
What we publish per ZIP
- Population (ACS 5-year)
- Median household income
- Median home value (owner-occupied)
- Median rent (renter-occupied)
- Median age
- Poverty rate
- Educational attainment (bachelor's+ rate)
- Homeownership rate
- Race and ethnicity breakdown
Cross-reference and verification
- Census Data Explorer — the official interface to ACS tables.
- ACS Data Releases — release schedule and methodology.
- USPS ZIP Code Lookup — the authoritative source for which ZIP serves a specific address.
- HUD-USPS ZIP Code Crosswalk — maps ZIPs to ZCTAs, counties, tracts, CBSAs.
Update frequency
The Census Bureau releases new ACS 5-year estimates each December. We refresh within days of each release.
Limitations you should know about
- ZCTA ≠ neighborhood. A single ZIP can span multiple distinct neighborhoods.
- 5-year averages. ACS 5-year smooths over a window, lagging actual change in fast-moving areas.
- Sampling error. Small ZIPs can have ±10-20% margins on income or poverty figures.
- PO box ZIPs not included.
- Not legal, financial, or real-estate advice.For decisions involving school enrollment, insurance, or property purchase, verify ZIP-specific facts with the relevant authority.
Corrections and feedback
If a published Census ACS figure disagrees with what you see here, please contact us with the ZIP and the Census source URL.
This methodology page was last reviewed in March 2026. Material changes to how we source or compute the data will be reflected here before they reach production pages.