realtor.com Real Estate Data Library — Core Inventory Metrics

Monthly figures from July 2016, the start of realtor.com's published history for this series, through the most recent release, at three geographies: counties, metropolitan and micropolitan areas, and ZIP codes.

Coverage is not even across those three. The county and metro files report every county and every core-based statistical area in every month. The ZIP file is uneven: many ZIP codes carry the full monthly history, some carry only a handful of months, and the most recent month does not cover every ZIP code realtor.com has ever reported. A ZIP code with very few homes for sale in a given month is the kind of place most likely to be thin or missing.

realtor.com does not publish figures for Puerto Rico at any of the three geographies.

The files are published for counties, metro areas and ZIP codes and are used at those grains directly: a county figure is realtor.com's county figure, unmodified.

Census tracts are not published by realtor.com. Where a tract-level reading is offered, it is assembled from the ZIP codes that overlap the tract, in the same way a home-value figure can be assembled from ZIP-level data — see Zillow Home Value Index for the general approach. ZIP codes here are the U.S. Postal Service's own 5-digit codes, not ZIP Code Tabulation Areas; most, but not all, ZIP codes correspond closely to a ZCTA of the same digits.

These are counts and durations drawn from active listings, not from closed sales, so they describe what is on the market rather than what changed hands. A market with few sales but many long-sitting listings and a market with few sales because almost nothing is listed can look similar on a sale-price measure and very different here.

The figures are nominal counts and day-counts; none of them are adjusted for inflation. Some are seasonal by nature — the number of homes for sale rises and falls with the time of year in most places — which is why the tool also offers a reading against a location's own seasonal norm rather than only against a year-over-year change.

realtor.com publishes this data as free downloadable research data and permits redistribution and commercial use subject to attribution to realtor.com. Figures derived from this data are our own; realtor.com is not responsible for our calculations.