Methodology

Data sources

• U.S. Census Bureau, American Community Survey (ACS) 5-year estimates. Median home value, median owner costs with and without a mortgage, median gross rent, property tax, household income, homeownership rate, and population, at the county level.
• FEMA National Flood Insurance Program (NFIP). Historical flood claims, average claim amount, active policy counts, and average premiums, aggregated to the county level to derive a flood-risk signal.
• FHFA House Price Index (HPI). Quarterly state-level home price appreciation. Used for 1-year and 5-year appreciation figures.
• IRS Statistics of Income (SOI). State-level averages for mortgage interest and property tax deductions claimed, and the share of returns claiming each deduction.
• DOE Energy Information Administration (EIA). State-level residential electricity and natural gas prices; estimated annual residential energy cost.
• HUD Fair Market Rents (FMR). County-level fair market rent by unit size, used to anchor rent-vs-buy comparisons.
• FRED (Federal Reserve Bank of St. Louis). Current 30-year fixed mortgage rate used as the default rate in calculators.

Key calculations

Annual ownership cost

Property tax (from Census ACS) + insurance estimate (county-adjusted baseline) + energy cost (from DOE EIA state averages) + maintenance (1% of home value). Presented as annual and monthly.

Rent-vs-buy break-even

Compares cumulative non-equity ownership outflows (interest, taxes, insurance, maintenance, closing costs) net of equity gained against cumulative rent net of the down-payment pool invested at an assumed market return. Break-even is the first year where net buy cost is less than or equal to net rent cost. Defaults: 20% down, 30-year mortgage, current FRED rate, 1% maintenance, 3% appreciation, 3% rent growth, 5% investment return.

Affordability index

Median owner cost (with mortgage) as a percentage of median household income (both from Census ACS). Lower is more affordable.

Flood-risk score

Derived from total NFIP claims in a county. Buckets: low (fewer than 10 claims), moderate (10 to 49), high (50 to 199), very high (200+). This is a historical signal, not a forward-looking forecast.

Update cadence

• Census ACS: annually, on release of new 5-year estimates.
• FEMA NFIP: monthly, using the latest open data export.
• FHFA HPI: quarterly.
• IRS SOI: annually.
• DOE EIA: quarterly or monthly depending on the series.
• HUD FMR: annually.
• FRED mortgage rates: weekly.

Limits and caveats

County averages hide intra-county variation. Property taxes, insurance premiums, and utility costs can vary widely between neighborhoods, home ages, and structures. Historical flood claims do not capture properties that were never insured. Figures on this site are starting points, not a substitute for a professional assessment of a specific property.