Research question
What does this evidence show within this research scope: Three complete Zillow city inventory series: Chicago, Elmhurst, and Glen Ellyn?
Returning from a low current count to an earlier level requires a larger percentage increase than the percentage decline measured from the earlier base.
Elmhurst inventory rose 23.08% from August 2025 to August 2026. Glen Ellyn rose 18.29%. Those increases did not return either city to its August 2019 count.
The reason is both factual and mathematical: the 2026 base is much smaller.
Decline and recovery use different denominators
Elmhurst declined from 362 active listings in August 2019 to 112 in August 2026, a 69.06% decline measured from 362. Returning from 112 to 362 would require a 223.21% increase measured from 112.
Glen Ellyn declined from 319 to 97, or 69.59%. Returning from 97 to 319 would require a 228.87% increase. Chicago declined from 11,533 to 5,576, or 51.65%; the reverse calculation from the 2026 base is 106.83%.
This asymmetry is a denominator effect. A 50% decline followed by a 50% increase does not return a count to its starting level.
A one-year rebound and a long-period deficit can coexist
The Elmhurst and Glen Ellyn series show both conditions at once. Inventory improved from 2025 but remained far below 2019. Chicago moved differently, declining 8.41% year over year while also remaining below 2019.
The earlier count is a comparison point, not a target or a normal level that the market must regain. The calculation does not predict whether inventory will rise, how quickly it could change, or which properties would make up any increase.
The reverse percentage is not a forecast
The 106.83% to 228.87% reverse calculations answer only how much the 2026 count would need to increase to equal the 2019 count mathematically. They do not say that such increases are likely or desirable. Listings enter and leave the market, and a city count can change with seller decisions, contract activity, withdrawals, expirations, and the provider's coverage. The calculation keeps the denominator visible; it does not model those flows.
A search still needs its own competitive set
City inventory counts include homes outside a buyer's exact property type, price, size, condition, and location criteria. A seller also competes with a narrower set than the whole city.
Use the baseline comparison to understand scale, then inspect active, pending, and recent closed properties that match the decision.
Source and method: Zillow seasonally adjusted city for-sale inventory. Reverse increase = (August 2019 inventory / August 2026 inventory - 1) x 100. Read the full complete-case study for the three included cities and documented exclusions.
Questions about this research
What question does this research answer?
It examines this scope: Three complete Zillow city inventory series: Chicago, Elmhurst, and Glen Ellyn. The research period is August 2019, August 2025, and August 2026. Returning from a low current count to an earlier level requires a larger percentage increase than the percentage decline measured from the earlier base.
Can this research set a price or offer for a specific property?
No. This is point-in-time research for the stated scope; a property-specific decision still requires current comparables, the property's condition, and the transaction facts that apply to the address.
Where can I review the method and limits?
The publication below identifies the source notes, reporting period, geography, and scope limits used for this analysis.