You just bought the house. You signed the contract, brought money to closing, and accepted the price. Then the assessment notice arrives with an estimated market value that looks wrong.
Quick Answer
A recent purchase does not disqualify an owner from appealing, and it does not guarantee a reduction. Closing price is evidence against estimated market value. It is not the 10% residential class calculation and not the Assessor’s 10% rule of thumb.
The trap is assuming you have no argument because you recently paid what you paid. A sale can be strong evidence of market value, but it does not waive your right to question an assessment. Nor does it guarantee that the assessment should fall. The closing price has to be considered for what it is: evidence from one transaction on one date.
Aaron Fox Law describes the familiar assumption that a recent buyer cannot appeal because the purchase price must have settled the value. That comes from an attorney-marketing article updated **2026-07-07**. It is outside commentary, not a Censum customer account. The official starting point remains the Cook County Assessor’s guidance: look at the characteristics on the notice and compare its estimated market value with what the home could sell for in the current market.
The confusion usually comes from mixing three different ideas. Two involve 10 percent. The third, your closing price, does not.
The first 10 percent is Cook’s residential class level
The Cook County Assessor defines assessed value as fair market value multiplied by the assessment level for the property’s class. For residential property, that class level is **10 percent**.
This is calculation language. The Assessor first places an estimated fair market value on the property, then the residential class percentage converts that estimate into assessed value. The 10 percent does not mean your tax bill equals 10 percent of the home’s value. It also does not mean the county must take exactly 10 percent of the number on your closing statement simply because a sale occurred.
Your deed price can inform the estimated market value. It is not itself the class percentage.
The companion Censum Sense article, **“What ‘Property Over-Assessed’ actually means,”** walks the Board’s **$250,000** example to **$25,000** assessed, **$75,750** EAV at tax year 2025’s **3.0300**, and **$65,750** after the full **$10,000** Homeowner cap. That path is the Board’s illustration, not the reader’s closing price, and it is not a 2026 notice figure. For a recent buyer, the question comes one step earlier: does the estimated market value hold up against the transaction and the rest of the market evidence?
The second 10 percent is the Assessor’s rule of thumb
The Assessor uses another **10 percent** figure when explaining whether an appeal is likely to matter. This one is not part of the class calculation.
Its rule of thumb says that when the property characteristics are correct and the estimated market value is within 10 percent of what you think the home is worth, an appeal is unlikely to change the assessed value enough to significantly affect the property-tax bill. That is a practical screen, not a second assessment rate.
Start by reading the property card as if you had never seen the closing price. Is the square footage right? Are the class, age, construction, occupancy, and other characteristics accurate? A factual error can support an appeal regardless of what changed hands at closing.
Then look at value. The Assessor’s owner-facing test asks whether its estimated market value is significantly more than what you believe the home could sell for in the current real estate market. A recent arm’s-length purchase may be highly relevant to that question. So may comparable sales, an appraisal, the contract, a deed, a transfer declaration, photographs, or facts showing that the transaction was unusual.
The rule of thumb helps you decide whether the gap deserves more work. It does not transform your sale price into an automatic answer.
Your closing price is neither 10 percent
A closing price is a dollar amount agreed upon by a particular buyer and seller. If the transaction was recent, arm’s-length, and below the Assessor’s estimated market value, the closing documents may support a lower market-value conclusion. Illinois Department of Revenue guidance specifically identifies a deed or contract and a Real Estate Transfer Declaration among the evidence an owner may use in an assessment appeal.
The same evidence can cut the other way. A strong recent sale may support the Assessor’s estimate or expose a gap in the owner’s lower opinion of value. Timing and transaction circumstances matter. If the transaction does not reflect an ordinary arm’s-length market sale, explain why before asking the number to carry much weight.
No 10 percent rule says a closing price automatically becomes the assessment, and none says buying the property bars an appeal. The sale belongs in the evidence file, not in place of the analysis.
New buyers can also be misled by the tax figure shown before closing. That bill reflects an earlier point in the property-tax cycle and may include exemptions tied to the prior owner’s circumstances. It does not establish what the new owner’s assessment or later bill must be. Purchase price, estimated market value, assessed value, exemptions, and the amount due are connected, but they are not interchangeable.
Build the argument around the property
If the assessment notice overstates what the home could sell for, show why. Put the closing documents beside the property record card and genuinely comparable sales. Explain any material feature the county record misses: condition, size, construction, location, or another characteristic that affects value. If the recent sale supports the Assessor instead, recognize that before spending time on a weak market-value claim.
At the Board of Review, the filing instructions call the complaint **Property Over-Assessed**. That wording keeps the issue focused. The Board reviews evidence about whether the proposed assessment is fair, accurate, and supported. It is not deciding whether the buyer regrets the price or simply dislikes the tax bill.
Do not wait for the bill to begin that review. The Illinois Department of Revenue says an owner appeals the assessed value rather than the tax bill, and once the bill arrives, it is generally too late to appeal that year’s assessment. Filing periods run by township, so the date attached to someone else’s property may not be yours. For Berwyn, Cicero, Elk Grove, Lakeview, Maine, and Palos, Group 2 closes **Tuesday, September 29, 2026**. The tax year 2025 second installment is still due **Thursday, October 1, 2026**; an appeal does not stop that payment. The Board says its decision is reflected on next year’s bill.
County officials set assessments and decide appeals; no result is guaranteed.
Sources
- Cook County Assessor, Overview of How Appeals Work
- Illinois Department of Revenue, Assessment Appeals
- Cook County Board of Review, How to File an Appeal Online
- Aaron Fox Law buyer article, attorney marketing updated 2026-07-07
- Censum FAQ
Sources accessed 2026-09-02.
FAQ
Can I appeal after I just bought the house?
Yes. A sale can be strong evidence of market value. It does not waive the right to question an assessment. Aaron Fox Law describes the “I just paid the price” assumption in attorney marketing updated 2026-07-07. That is not a Censum customer account. The Assessor’s appeals page is the official test.
Is the 10% class level the same as the 10% rule of thumb?
No. Cook’s residential class level is 10% of estimated fair market value. The Assessor’s 10% rule of thumb is a separate screen: if the card is right and estimated market value is within 10% of what you think the home is worth, an appeal is unlikely to move the bill much.
Is the Board’s $250,000 example my closing price?
No. In that Board illustration a $250,000 home is $25,000 assessed, $75,750 EAV at tax year 2025’s 3.0300, and $65,750 after the full $10,000 Homeowner cap. Those figures are not a 2026 notice multiplier and they are not your deed price.
Does Censum file the appeal for me?
No. Censum LLC is a data and analytics company, not a law firm and not a tax advisor. You file your own appeal.
Next step
Look up your PIN. Compare estimated market value with the closing documents and the property card. If you are in Group 2, the Board window closes Tuesday, September 29, 2026. Pay October 1 anyway.
Censum LLC is a data and analytics company, not a law firm and not a tax advisor. You file your own appeal. Censum is independent and is not affiliated with Cook County or any government agency.