The four-city gap ranged from 7.3% to 23.4%, but it reflects two different statistical populations rather than an error band for a home.
A monthly sale median and a home-value index can both be valid while showing different dollar levels. In July 2026, Zillow's median sale price was above its all-homes ZHVI in each of the four reviewed cities.
The gaps were 20.67% in Chicago, 9.48% in Elmhurst, 7.25% in Glen Ellyn, and 23.36% in Hinsdale. Those percentages are not a correction factor.
A median describes the homes that sold
The median sale price is the middle price among the relevant reported sales. If the month's completed transactions contain a larger share of expensive homes, the median can rise even when no individual property's value changes by the same amount.
The public city file used here does not provide the transaction distribution or a matched set of homes. That prevents the analysis from assigning the gap to property type, size, condition, location, or another cause.
ZHVI describes a broader modeled stock
Zillow describes its middle-tier ZHVI as a modeled typical value for homes in the 35th to 65th percentile range. Its current methodology is intended to track the broader housing stock instead of only the homes sold during one month.
That difference in population is the main lesson. A transaction statistic can be affected by which homes traded. An index is constructed to answer a different market-level question.
Do not turn the gap into an offer rule
Chicago's $400,000 sale median was $68,530 above its July ZHVI. Hinsdale's $1,587,500 sale median was $300,581 above its index. Neither result says a buyer should add that amount to an automated estimate or that a seller should expect it.
An individual pricing decision needs recent comparable properties, current competition, condition, size, location, features, price history, concessions where available, and timing. The city comparison only explains why two broad price headlines should retain their definitions.
The complete-case rule keeps the comparison honest
The retained median-sale-price file had exact rows for four of the six cities reviewed elsewhere in this research library. Western Springs and Clarendon Hills were not present, so this article does not borrow a county result or substitute a nearby place. July is used because it is the last date in the retained sale-price file, while the matched ZHVI observation is taken from that same month. Keeping those boundaries visible is more useful than presenting a larger but mixed sample.
Source and method: Zillow city all-homes ZHVI and city median sale price, matched on July 31, 2026. Read the full four-city study for exact values, exclusions, formulas, downloads, and source links.