What a winning property tax appeal is actually worth
Across 408,796 successful Cook County appeals, the median reduction was 8.4% of assessed value. Here is what that means in dollars, and whether it is worth your evening.
Advertising for appeal services tends to lead with the largest number available: a case where somebody saved thousands. That case exists. It is not typical, and knowing what typical looks like is the difference between a reasonable decision and a disappointed one.
The Cook County Assessor publishes the assessed value before and after every appeal it decides. Across 408,796 appeals that produced a reduction, here is the distribution.
A quarter of successful appeals cut less than 5.7% of assessed value. Half cut less than 8.4%. A quarter cut more than 14.3%.
Turning that into money
A percentage of assessed value is not a number anyone can act on. Here is the full chain for a Cook County home the assessor believes would sell for $300,000.
| Step | Before | After an 8.4% reduction |
|---|---|---|
| Assessed value (10% of market) | $30,000 | $27,480 |
| × equalisation factor 3.0355 | $91,065 | $83,415 |
| − homestead exemption | $81,065 | $73,415 |
| × composite rate 7.5% | $6,080 | $5,506 |
The multiplier most people forget
A reduction is not a one-year benefit. It generally holds until your next reassessment — three years in Cook County, four in most other Illinois counties.
Where the rate changes everything
The $574 above uses a mid-range Cook composite rate. Real rates in the county run from roughly 6.5% in parts of Chicago to over 20% in some south suburban areas.
| Composite rate | Annual saving on the same reduction | Over a 3-year cycle |
|---|---|---|
| 6.5% | $497 | $1,492 |
| 7.5% (mid-range) | $574 | $1,721 |
| 12% | $918 | $2,754 |
| 20% | $1,530 | $4,590 |
Use the rate on your own bill. Any figure calculated with a county-wide average — including ours — is an illustration rather than a forecast for your parcel.
The expected value calculation
Combine the chance of winning with what a win is worth.
County-wide, 23% of decided appeals produced a reduction — though this varies from 30.6% in Jefferson Township to 7.6% in Palatine, and has fallen from 31.9% in 2021 to 16.2% in 2025.
That is roughly $110 an hour, tax free, on a task most people can do. It is a perfectly good use of an evening. It is not the windfall the advertising implies.
Why the downside is small
At the Cook County Assessor stage an appeal cannot raise your assessment. The worst outcome is no change, so the risk is your time rather than your money.
The Board of Review can raise as well as lower, though in practice rarely does for residential property — and when it does, it is generally on evidence the appellant supplied, most often a recent purchase price above the county's implied value.
When it is worth more than this
High-rate areas. Three times the benefit at 20% against 6.5%.
Larger properties. The percentages hold; the dollars scale.
Early in a reassessment cycle. Three years of benefit rather than one.
Where the disparity is large. The median is 8.4%, but a quarter of wins exceed 14.3%. If your property is 25% above tight comparables, you are not aiming at the median.
When it is worth less
Low-rate areas with a marginal case.
Late in a cycle, when the correction is reset almost immediately.
Paying a third of it away. A contingency firm taking a third of the first year's saving takes roughly $190 of a $574 benefit — for an advantage the county's own data cannot reliably detect on ordinary residential appeals.
The honest summary
A typical successful Cook County appeal is worth a few hundred dollars a year, recurring for the cycle, on roughly a one-in-five chance. Worth doing when the arithmetic says you have a case. Not worth doing speculatively, and not worth paying a third of.
Check your exemptions first. A Cook homestead exemption is worth around $750 a year, is granted on an application rather than won on an argument, and beats the median appeal outright.