About this tool
A free, independent estimator built for one specific moment: your Cook County property was reassessed and you want to know what you actually owe — and whether you might be over-assessed.
Why we built it
General property-tax calculators are built for nationwide comparisons, not the specific question homeowners ask when a reassessment notice arrives: "my assessed value changed — what does that mean for my bill, and is it fair?" This tool answers that question for Cook County, Illinois, using the same chain of math the County itself uses to produce a bill.
The methodology
Your estimate follows the exact Cook County Class 2 (residential) tax chain:
- Your assessed value (already at the County's 10% assessment level) is multiplied by the Illinois Department of Revenue's annual state equalization factor.
- That produces your Equalized Assessed Value (EAV).
- Eligible exemptions (Homeowner, Senior, Disabled Person, Veteran exemptions) are subtracted.
- The result is multiplied by your local composite tax rate — the combined rate of every taxing district that overlaps your specific tax code (your school district, municipality, park district, and so on).
Composite rates and the state equalizer come from PTAXSIM, the Cook County Assessor's own public simulation database, not from outdated or generic state averages. We do not model certain special-case items — TIF district increment diversion, Special Service Area levies, Senior Freeze (a base-year cap rather than a flat reduction), and certificate-of-error/PTAB adjustments — and we say so plainly in the estimate.
How we know it's accurate
We don't just trust our own math — we checked it against reality. We pulled a sample of real Cook County residential parcels, computed what this tool says they should owe, and compared that against the actual published bill from the Cook County Treasurer for those same parcels. The estimate reconciles within ±2% of the real published bill for the large majority of that sample (most cases match to within a few dollars). The misses are concentrated in the special-case items listed above, which is exactly what the methodology predicts and discloses.
Latest backtest: 94.8% of 346 real Tax Year 2023 Treasurer bills within ±2%, as of July 1, 2026. Error figures reflect backtesting as of this date and are updated when the test is re-run.
What this tool is not
This is an independent educational project. It is not affiliated with, endorsed by, or operated by the Cook County Assessor, Clerk, or Treasurer. It does not file appeals, represent you before any government body, or guarantee any outcome. It is not tax or legal advice — see the disclaimer on every page. Always verify your specific numbers with the official County offices before making a financial decision.