Zillow, Realtor.com, Redfin and Illinois REALTORS show different Chicago prices. Definitions and reporting windows explain why they are not interchangeable.
Source populations and reporting periods differ.
A Chicago buyer can encounter several credible housing-price figures without any of them answering exactly the same question. The problem begins when those figures are treated as interchangeable estimates of one universal market price.
At retrieval, Zillow displayed a typical home value of $334,030 through August 31. Realtor.com's city summary displayed a median sold price of $390,000. Illinois REALTORS reported an August city median sale price of $405,000. Redfin displayed $426,255 in its three-month period ending August.
These are four different statistical observations. Their spread is not a negotiating range, a valuation error estimate or evidence that one company has discovered a hidden discount.
A modeled value is not a closed-sale median
Zillow's Home Value Index is a modeled value series. A transaction median comes from properties that actually sold within a defined population and period. Those sold properties need not have the same composition as the housing stock represented by a value index.
A change in which homes transact can move a sales median even when no individual property's value changes by the same amount. That is one reason a median-price increase should not automatically be described as appreciation for every owner.
The reporting window also matters. Redfin's text describes three months ending in August, while the Illinois REALTORS PDF describes August itself. Realtor.com's retrieved city summary carries a September heading while its charts run through August. The ambiguity is retained in this analysis rather than silently assigning it a completed September period.
The asking-price comparison creates a second trap
Realtor.com's displayed listing median was $385,000, which was $5,000 below its displayed sold median. The difference is approximately 1.3% of the listing median.
That does not mean the typical buyer paid 1.3% above asking. Listing and sold medians describe different groups of properties. A matched-property sale-to-list calculation asks a different question: how did each completed transaction's price compare with that same property's relevant asking price?
Even that measure needs a definition. Original and final asking prices can differ. Credits and concessions can alter the transaction's economics without appearing in a simple price comparison.
Choose the measure that answers the decision
A buyer preparing an offer needs comparable transactions, the subject property's pricing history, current alternatives and the terms of those deals where available. A citywide median cannot do that work.
A seller needs evidence about both successful transactions and current competition. A modeled value trend can provide context, but it should not replace a property-specific analysis of condition, size, location and timing.
For a market article, the practical rule is to attach a definition, geography and period to every headline number. If two sources differ, investigate those dimensions before concluding that one is wrong. If their boundaries cannot be reconciled, keep the results separate.
Chicago's different price headlines are therefore most useful as a lesson in measurement. They show why a carefully defined question produces a more useful answer than a search for one definitive citywide home price.
Sources: Zillow Chicago, Realtor.com Chicago, Redfin Chicago, and Illinois REALTORS August city report. No blended price index or property valuation is calculated.