Zillow Home Value Index
A monthly index of typical home value, published by Zillow for metro areas, counties and ZIP codes from a valuation of every home rather than only the ones that sold.
The Zillow Home Value Index measures "the typical home value" in an area, which Zillow describes as "a smoothed, seasonally adjusted measure" (Zillow Home Value Index Methodology, 2019 Revision).
What distinguishes it is its base. A median sale price describes the homes that changed hands; ZHVI is built from Zillow's valuation of every home in an area, whether or not it sold. The 2019 revision's stated purpose was to remove the mix effects that follow from the first approach — an index that moves because the market sold more expensive houses this quarter, rather than because houses became more expensive.
That makes the index useful at small geographies and in quiet months. It also makes it a model output, not an observation: every figure rests on Zillow's per-home valuations, and their errors travel into the index. The main cut used here is all homes — single-family and condominium together — in the 33rd to 67th percentile tier; separate condo-only and bedroom-count cuts are also published, documented on their own pages.
Coverage#
Monthly values from January 2000 through the most recent release, at three geographies: metropolitan and micropolitan areas, counties, and ZIP codes.
Coverage today is much better than coverage in history. Roughly 3,071 counties carry a recent value, but only about 1,066 reach back to 2006 and 710 to 2000. A one-year change is therefore available in far more places than a ten-year one, computed over a smaller, differently distributed set of places.
Coverage is not universal today either: roughly 7,000 ZIP codes have too little activity for Zillow to publish a value. Zillow revises history with each monthly release.
Geography#
The files are published for whole metro areas, counties and ZIP codes and are used at those grains directly: a county figure is Zillow's county figure, unmodified.
Census tracts are the exception, because Zillow publishes nothing at tract level. A tract's value is assembled from the ZIP codes that overlap it, each weighted by the housing units the two share — not by population, because a tract's home value should be the value of its homes, and weighting by residents hands a tract's price to whichever overlapping area holds the most people.
Where the overlapping ZIP codes have no published value, the tract is left blank rather than filled from the surrounding county or metro. A missing ZIP code price is not a neutral gap — the ZIP codes Zillow cannot price are systematically unlike their county's average — so a county figure standing in would be a confident guess about exactly the places least suited to it.
ZIP codes are handled as ZIP Code Tabulation Areas, the census geography built from the ZIP codes of the addresses inside it — close to, but not identical with, the postal ZIP code of the same digits.
Other considerations#
The index is nominal and is not adjusted for inflation. It is seasonally adjusted and smoothed, so a single month's reading is not an independent observation of that month.
Because ZHVI is expressed in dollars, its levels are comparable between places — unlike a repeat-sales index normalized to each area's own base year. That is why it supports a level measure at all, where FHFA's repeat-sales index supports only rates of change.
Metrics built on this source#
Citation#
Data Provided by Zillow Group
Zillow's terms permit non-personal use of the aggregate data, including derivative works, provided the Zillow Companies are credited on every page displaying the data, no Zillow logo is shown, and no relationship or endorsement is implied (Zillow Group Terms of Use). Figures derived from this index are our own; Zillow is not responsible for our calculations.
References#
- 1Zillow Research Datahttps://www.zillow.com/research/data/
- 2Zillow Home Value Index Methodology, 2019 Revisionhttps://www.zillow.com/research/zhvi-methodology-2019-deep-26226/
- 3Zillow Group Terms of Usehttps://www.zillowgroup.com/developers/api/public-data/real-estate-metrics/