What we do differently
Every estimate on this site is grounded in three publicly available datasets from data.ny.gov:
- Property Assessment Rolls — the actual parcel record for your address, including the county’s assessed full market value, school district, and property class. We currently index every Nassau and Suffolk residential parcel.
- Real Property Tax Rates by Municipality — current millage rates for every county / town / school combination, expressed per $1,000 of full market value.
- Equalization Rates — the conversion factor used in Suffolk where towns assess at a fraction of full value. We back-derive full market value from assessed value when the state doesn’t report it directly.
The calculation
For each parcel, we look up the most recent rates for its specific town SWIS code and school district code (these can differ from what the parcel filing shows — Nassau parcels file under village SWIS codes, but rates are filed at the town level). The combined rate is the sum of:
Combined rate, per $1,000 of full market value
- County rate
- +Town rate
- +School district rate
- +Village rate If the home is in an incorporated village
- +Special district rates Fire, library, water, sewer and so on
Estimated bill = full market value × combined rate ÷ 1,000
Confidence levels
Every estimate is tagged with a confidence level so you know what you’re looking at:
- HIGH — parcel matched, current rates loaded, all five components present.
- MEDIUM — parcel matched, state-level rates loaded, but village rates and per-parcel special district rates are still being ingested. Your actual bill may be 5–15% higher in incorporated villages.
- LOW — parcel found but with incomplete data. Treat the number as a rough ballpark, not a quote.
Sale price vs. assessed value
Nassau systematically under-assesses homes — assessed value typically lags current market price by 15–30%. If you enter your sale price, we project what your bill will become as the assessment catches up over a 3–5 year reassessment cycle. This isn’t a guarantee of the future — it’s a projection based on Nassau’s typical reassessment behavior since the 2020–21 cycle.
What’s not in our estimate
We don’t yet ingest:
- Village-specific tax rates (~95 incorporated villages)
- Per-parcel special district line items (fire, library, sewer, sanitation, ambulance)
- Co-op apartments — these don’t have individual tax bills under NY law
- Commercial properties — out of scope for this tool
We also don’t apply your specific exemptions automatically. The “Exemptions you can stack” section on each result page shows what you might qualify for — applying still happens through your county assessment office.
Refresh schedule
State assessment rolls publish a tentative version on May 1 and a final version around July 1 each year. We re-pull weekly. Rate data updates annually — Nassau publishes the new year’s rates each December; Suffolk by late January.