What this calculator does
Cook County's property tax formula has more steps than most. This calculator walks through each one — assessment level, the state equalizer, exemptions and the composite rate — so you can see how a market value becomes a bill. Cook County taxes residential property on 10% of market value, multiplied by the state equalization factor (3.0300 for 2025), minus exemptions such as the $10,000 homeowner exemption, then times the composite rate of every district on your tax code. Chicago's effective rate often lands around 2% of market value.
How to use it
- Enter the Assessor's market value (from your notice or the Assessor's website).
- Tick the exemptions you have.
- Enter the composite tax rate printed on your latest second-installment bill.
The formula
Tax = ((market value × 10%) × equalizer − exemptions) × composite rate. The equalizer for 2025 is 3.0300.
Worked example
Using the default inputs shown in the calculator above:
| Step | Amount |
|---|---|
| Market value | $350,000 |
| Assessed value (10%) | $35,000 |
| Equalized assessed value (x 3.0300) | $106,050 |
| Exemptions (EAV) | -$10,000 |
| Taxable EAV | $96,050 |
| Tax at composite rate 7.000% | $6,724 |
| Estimated yearly tax | $6,724 |
Estimated Cook County property tax: $6,724. Effective rate 1.92% of market value · exemptions save $700.
Cook County taxes only 10% of market value, but the state equalizer (3.0300) roughly triples it before exemptions come off. Because exemptions are subtracted from equalized value, the $10,000 homeowner exemption saves about $700 a year at this rate.
What moves a Cook County bill
Reassessments happen every three years by area (the City of Chicago, north suburbs and south suburbs in turn), and appeals go first to the Assessor and then to the Board of Review. The composite rate differs by tax code because each combination of school, park, library and special districts is different. Seniors can also apply for the senior assessment freeze.
Common mistakes and tips
- Using the sale price instead of the Assessor's market value.
- Forgetting that exemptions come off equalized value, not market value.
- Missing the appeal window after a reassessment notice.
- Not applying for exemptions after buying — new owners must apply.
Frequently asked questions
What is the Cook County equalizer for 2025?
3.0300, announced by the Illinois Department of Revenue.
How much does the homeowner exemption save?
It removes $10,000 of equalized value, so at a 7% composite rate it saves about $700 a year.
Why is my bill paid in two installments?
The first installment is 55% of the prior year's bill; the second reflects the new assessment, rates and exemptions.
How do I appeal?
File with the Cook County Assessor during your township's appeal window, then with the Board of Review if needed.
Sources
Disclaimer
This calculator provides estimates for educational purposes only and is not financial, tax, legal, real estate, or insurance advice. Consult a licensed professional before making decisions.