Sources & methodology
Where our numbers come from, how the calculators work, how we handle the messy edges of public data, and when the dataset is refreshed.
Primary data sources
Every state and ZIP-level number on this site traces back to one of these public sources. None of the data is hand-curated, scraped, or pulled from private aggregators.
- US Census Bureau — American Community Survey (ACS), 5-Year
Estimates. Current vintage: ACS 2019–2023
(released December 2024). We pull three tables:
-
B25103_001E— Median Real Estate Taxes Paid (housing units with a mortgage). Used for ZIP-level median property tax. -
B25077_001E— Median Home Value (owner-occupied housing units). Used as the denominator in effective-rate calculations. -
B19013_001E— Median Household Income. Used in tax-burden-as-share-of-income comparisons on per-state pages.
-
- Tax Foundation — state-level effective property tax rate rankings used as a cross-check against our Census-derived state medians. We cite their figure when our derivation and theirs converge; we explain the gap when they don't. taxfoundation.org/data/all/state/property-taxes-by-state.
- State revenue authorities. Per-state pages cite the relevant state agency for assessment cycles, exemption rules, appeal deadlines, and relief programs. Each state page lists the agencies it draws from at the bottom of the page.
Formulas
The calculators are intentionally transparent. Each one shows its formula on the page, and the math runs entirely in your browser — we do not transmit, log, or store your inputs.
- Effective tax rate = Annual property tax paid ÷ Home market value
- Mill rate → annual tax = (Mill rate ÷ 1,000) × Taxable assessed value
- Homestead savings = Exemption amount × Effective tax rate
- Escrow monthly = (Annual property tax + Annual homeowners insurance) ÷ 12, with a RESPA-compliant 2-month cushion typically held by the servicer
- Cumulative projection = Year-1 tax compounded at an assumed annual growth rate, summed over the projection horizon
- Relocation delta = (Destination effective rate − Origin effective rate) × Home value, compounded over the ownership horizon
How we handle Census topcoding
The ACS caps three numeric fields at fixed ceilings to preserve respondent privacy in high-value or high-income ZIPs. The cap value is published in the data with a fixed sentinel one above the cap. We surface this honestly on each per-ZIP page rather than displaying point estimates that the data does not support.
| Field | Cap | How we display it |
|---|---|---|
| Median real estate taxes (B25103) | $10,000 | ≥X.XX% (floor on the effective rate) |
| Median home value (B25077) | $2,000,000 | ≤X.XX% (ceiling on the effective rate) |
| Median household income (B19013) | $250,000 | ≤X.X% (ceiling on burden share) |
| Both tax and value topcoded | — | — indeterminate; the directional comparison is suppressed |
Topcoding is more common than most aggregator sites admit. In our current dataset (29,350 ZCTAs):
- NJ — 44% of ZCTAs hit the tax topcode (the state median tax is $9,590, so most ZIPs end up at the $10,001 sentinel)
- CA — 10% topcoded; CA Bay Area and LA Westside have ZIPs where both tax and home value are topcoded
- TX — 3% topcoded
- FL — 0.8% topcoded
Update cadence
The Census ACS 5-Year Estimates are released annually in mid-December. The dataset on this site is refreshed once per cycle:
- Current vintage: ACS 2019–2023 (released Dec 2024, in use here since April 2026)
- Next refresh: ACS 2021–2025 vintage, target mid-December 2026
Per-state pages also reflect state-level statutory changes (assessment cycle, exemption thresholds, relief-program eligibility) and are reviewed alongside each data refresh.
What our numbers are not
The values on this site are medians, not household-specific estimates. Two homes on the same street with the same assessed value can owe materially different property tax due to homestead status, senior/veteran exemptions, special-district overlays (MUD, PID, Mello-Roos, fire-protection, school-bond), and recent reassessment events. Use our calculators to set expectations and compare jurisdictions; use your county assessor's website to check your specific parcel.
Tax Bill Tools is not tax, legal, or financial advice. Decisions with real money on the line — filing an appeal, moving between states, restructuring debt, claiming an exemption — warrant a licensed professional in your state.
Reporting a data correction
If you spot a number that disagrees with your county assessor's published record, please email questions@taxbilltools.com with the ZIP, parcel address (or county tax-ID), and a link to the assessor record. Corrections that are verifiable against the underlying public dataset are folded into the next refresh.