Tax caps (PTELL): what they limit, and what they do not
PTELL limits how fast a taxing body's total levy can grow. It does not cap your individual bill.
The Property Tax Extension Limitation Law — tax caps — applies in Cook, the collar counties and other counties that have adopted it.
What it limits
The growth of a taxing body's total extension, generally to the lesser of 5% or the increase in the Consumer Price Index, without voter approval. It is a limit on the district's aggregate levy.
What it does not limit
Your individual bill. If your assessment rises faster than your neighbours', your share of a capped levy grows and your bill rises even though the district's total obeyed the cap.
Why this matters to an appeal
It is the clearest illustration of why uniformity is the real question. Under a cap the pool is close to fixed, so property tax becomes explicitly a question of shares. An assessment out of line with comparable properties is not an abstraction — it is a larger slice of a fixed pie.
Exceptions
New construction is outside the cap, as are debt service on referendum-approved bonds and levies approved by voters. This is why a district with heavy new development can grow its extension faster than the cap suggests.