Methodology

Property tax (tiered)

Tier 1 (all counties): effective rate = ACS median real estate taxes paid (B25103) ÷ ACS median home value (B25077). Estimated tax ≈ home value × effective rate. Worked example: a $300,000 home at a 1.2% effective rate ≈ $3,600/yr. Tier-1 confidence is capped at Medium.

Tier 2 (where free county data exists): assessed value × mill rate − exemptions, honoring assessment ratios and caps. Tier 3: special districts / local levies.

Reassessment at purchase

We model the typical bill (current owners, median-based) against the estimated bill at your purchase price only where a transfer rule has been reviewed against an official state source. Launch coverage includes California Proposition 13 and Florida Save Our Homes. States without a reviewed rule do not receive a reassessment page.

Homeowners insurance budget

The baseline is the NAIC 2022 state average premium for an HO-3 policy. We scale that historical benchmark by the ratio between the selected home value and the county median home value, then apply a bounded FEMA National Risk Index county factor. The displayed range is deliberately wide (±40%). It is a Low-confidence budgeting estimate, not a carrier quote and not a prediction of a specific property's premium.

Mortgage and PITI

Principal and interest use the standard fixed-rate amortization formula. Monthly property tax is annual estimated tax ÷ 12; monthly insurance is the annual insurance budget ÷ 12. The default example assumes 20% down, 6.5% interest, and a 30-year term. The calculator accepts a user-entered rate and HOA amount. It does not yet model mortgage points, closing costs, flood insurance, maintenance, utilities, or property-specific exemptions.

Confidence rubric

• High: county-specific assessment data, recent, cross-source agreement.
• Medium: ACS-derived county rate (Tier 1), within the freshness window.
• Low: stale data, uncertain rules, or missing local inputs.

Confidence decays as data ages past its source's refresh cycle.

Sources & freshness

Sources: the estimates draw on these public datasets —

• U.S. Census Bureau — ACS table B25103 (median real estate taxes paid) — Median real estate taxes paid (baseline effective-rate numerator) (annual).
• U.S. Census Bureau — ACS table B25077 (median home value) — Median home value (baseline effective-rate denominator) (annual).
• NAIC — Homeowners Insurance Report — Average homeowners premium by state & policy form (HO-3) (annual).
• FEMA National Risk Index (OpenFEMA) — Natural-hazard risk (flood, wildfire, etc.), expected annual loss (on_release).
• California State Board of Equalization — Proposition 13 — California base-year value, change-of-ownership reassessment, and annual inflation cap (varies).
• Florida Department of Revenue — Save Our Homes assessment limitation — Florida change-of-ownership reassessment and homestead assessment-growth limitation (varies).

See the complete data-source register and limitations.

Methodology reviewed as of 2026-06-21.