Data Methodology
Every metric on GovCalculator is derived from official U.S. government public datasets. No proprietary models. No estimates. Every number traces back to a primary source.
Updated Jun 19, 2026 · Dataset v2 · HUD FY2026 · FMR FY2026 · IRS 2025 · BLS CPI-U 2013–2025
HUD — U.S. Department of Housing and Urban Development
Income Limits (Section 8)
HUD publishes annual income limits for the Section 8 Housing Choice Voucher program. Limits are broken into three tiers — Extremely Low (30% of Area Median Income), Very Low (50% AMI), and Low (80% AMI) — each adjusted for household size from 1 to 8 persons. GovCalculator embeds these limits per county in the master dataset under the incomeLimits field.
Fair Market Rents (FMR)
HUD also publishes annual Fair Market Rents — the 40th percentile gross rent for standard quality units in a local housing market. GovCalculator uses the 2-bedroom FMR (fair_market_rent_2br_usd) as the primary affordability reference for each county. The FMR fiscal year may differ from the income limits fiscal year; both are captured separately in the dataset manifest.
Section 8 Reference Limit
GovCalculator surfaces a derived Section 8 income reference threshold (section8_limit_usd) based on the 50% AMI limit for a reference household size. This value is informational and should not be used as a final eligibility determination without consulting the local Public Housing Authority.
IRS — Internal Revenue Service
Publication 15-T — Federal Income Tax Withholding
GovCalculator embeds the federal withholding tables from IRS Publication 15-T into each county record under the taxData field. The tables include the percentage method brackets for each filing status (Single, Married Filing Jointly, Head of Household, etc.).
Because federal withholding is uniform across all U.S. counties, the same IRS payload is replicated into every county record. This design allows each county page to render a complete federal tax context without any runtime API call. State income taxes are not included.
BLS — Bureau of Labor Statistics
CPI-U National Series (CUUR0000SA0)
The Consumer Price Index for All Urban Consumers (CPI-U) measures the average change in prices paid by urban consumers for a market basket of goods and services. GovCalculator uses the national CPI-U series (CUUR0000SA0) to compute inflation-adjusted purchasing power comparisons on each county page.
The BLS series is embedded as a snapshot of monthly data points covering the full coverage window (see Data Sources for the exact range). The formula applied is:
Adjusted Income = Nominal Income × CPI(to) / CPI(from)
This is a historical adjustment, not a forecast. No interpolation is applied; months not present in the embedded series are not used.
Why data is embedded in county records
Each county record in the GovCalculator master dataset is self-contained. It embeds the HUD income limits and FMRs specific to that county, the uniform IRS withholding tables, and the national BLS CPI-U series — all in a single JSON record.
- Deterministic rendering: the same input always produces the same output. No external API calls at render time.
- Full static generation: all 3,161 county pages are pre-rendered at build time, enabling fast delivery from a CDN with no server required per request.
- Auditability: the dataset build process is reproducible and the manifest captures exactly which source versions were used.
Update frequency
| Source | Official cadence | GovCalculator update |
|---|---|---|
| HUD Income Limits | Annual (fiscal year, typically April) | On next dataset build after HUD release |
| HUD Fair Market Rents | Annual (fiscal year, typically October) | On next dataset build after HUD release |
| IRS Publication 15-T | Annual (January) | On next dataset build after IRS release |
| BLS CPI-U | Monthly | Embedded as snapshot; updated with dataset rebuild |
Known limitations
Six states absent from county dataset
Connecticut, Massachusetts, Maine, New Hampshire, Rhode Island, and Vermont are not included. HUD uses town-based (not county-based) geography for these states, making direct county-level mapping impractical.
BLS CPI-U is a national average
The embedded inflation series reflects national urban price trends. It does not capture local price variation. County-specific CPI data is not publicly available at this granularity.
IRS tables cover federal withholding only
State income taxes, local taxes, Social Security, Medicare, and other payroll deductions are not modeled. The purchasing power module uses gross income adjustments only.
Median income is HUD-derived
The Area Median Income (AMI) figures used for income limits come from HUD's methodology, which differs from Census Bureau ACS estimates. Do not mix these figures with other AMI sources without adjustment.
Pages reflect the build-time dataset snapshot
County pages are statically generated from the dataset available at the last build. They do not reflect mid-year HUD or BLS updates until the next dataset rebuild and deployment.