The six-city historical annualized rates ranged from 3.56% to 6.63%. They compress 79 monthly intervals and do not predict the next one.
A long-period percentage can be annualized to make paths easier to compare. That calculation is a description of the period that already happened, not an expected return.
Across the 79 monthly intervals from January 2020 to August 2026, the historical annualized rates were 3.56% for Chicago, 5.52% for Elmhurst, 6.36% for Hinsdale, 6.45% for Glen Ellyn, 6.63% for Western Springs, and 6.55% for Clarendon Hills.
Annualization compresses an uneven path
The calculation asks what constant compounded annual rate would connect the first and last index levels. Actual monthly changes did not occur at one constant rate. The number hides the timing and size of changes between the endpoints.
Formula: (August 2026 ZHVI / January 2020 ZHVI) raised to 12/79, minus 1.
Changing either endpoint changes the result. A period beginning before, during, or after a sharp market move can produce a different annualized rate even for the same city.
Historical ranking is not future ranking
Western Springs had the highest annualized result in this six-city period. That does not establish that it will lead the sample next year, and the narrow difference from Clarendon Hills or Glen Ellyn is not a forecast advantage.
Interest rates, available inventory, household demand, new supply, property mix, and local conditions can change. The index itself can also be revised. Projecting the historical rate forward would add an assumption not supported by the source.
Period selection changes the summary
The January 2020 starting point was chosen to compare all six cities from one common date. It is not claimed to be a market cycle boundary or a buyer's purchase date. Starting one year earlier or later would change both the total and annualized results. A careful comparison therefore states the endpoints and number of monthly intervals instead of presenting the rate as a timeless characteristic of a city.
Use the rate as context, then return to the property
For a buyer, the rate can summarize how broad city indexes differed over a selected history. It cannot estimate the future value of a planned purchase. For a seller, it does not replace direct recent comparables and current competition.
Source and method: Zillow city all-homes ZHVI, January 31, 2020 through August 31, 2026. Read the full six-city study. No forecast, confidence interval, or property-level return was calculated.