Methodology
What ZHVI is
The Zillow Home Value Index (ZHVI) estimates the typical value of homes in the 35th–65th percentile range. We use the "all homes" series (single-family residences plus condos/co-ops), smoothed and seasonally adjusted, published monthly at the county level.
Formulas
- % change over h months = (V_t / V_(t−h) − 1) × 100
- Annualized = ((1 + c)^(12/h) − 1) × 100, where c is the cumulative change as a fraction
- Year-over-year uses the same county and the month exactly 12 months earlier
Missing months are never interpolated. Any change requiring a missing month is "unavailable" and shown in the No-data color — never as zero.
Price-Only inflection signals
r12 = 12-month change, r3 = latest 3-month change, p3 = previous 3-month change, acceleration = r3 − p3 (percentage points).
- A · Potential Recoveryr12 < 0, r3 > 0, acceleration > 0
- B · Early Warningr12 > 0, r3 < 0, acceleration < 0
- C · Accelerating Uptrendr12 > 0, r3 > 0, p3 > 0, acceleration ≥ +0.25pp
- D · Accelerating Downturnr12 < 0, r3 < 0, p3 < 0, acceleration ≤ −0.25pp
- E · Potential Peakr12 > 0, 0 ≤ r3 < 0.5%, acceleration ≤ −0.25pp
- F · Potential Bottomr12 < 0, −0.5% < r3 ≤ 0, acceleration ≥ +0.25pp
Evidence score 0–100 combines persistence across months, size of acceleration, market size & history length, and the category's retrospective reliability. It is not a probability — labeled "Evidence (Price-Only)".
Retrospective validation caveats
The validation panel is computed on today's revised ZHVI history, not point-in-time data; ZHVI history is revised each month. It counts new signals only. Past patterns do not imply predictive power.
Signal Performance Leaderboard
The Signal Performance Leaderboard scores each class (A–F) on every new signal: hit rate at 3, 6 and 12 months (value moved in the signal's direction), median and mean forward change, and excess change versus the median of all counties over the same months. Classes are ranked by 12-month excess hit rate. Breakdowns by period (2000–07, 2008–12, 2013–19, 2020–present), county value tier (terciles at the signal month) and county size are shown; any cell with fewer than 30 scored signals is marked insufficient. It is RETROSPECTIVE and price-only — not a forecast and not investment advice.
ZIP code detail
When you zoom in (about zoom level 7 and closer), the map switches to ZIP-code detail using Zillow's ZIP-level ZHVI — the same all-homes, mid-tier, smoothed, seasonally adjusted series as the county data, with the same color scale, saturation and comparison periods. Shapes are U.S. Census Bureau 2020 ZIP Code Tabulation Areas (ZCTAs). ZCTAs approximate USPS ZIP code delivery areas; they are not identical, and some ZIP codes (PO boxes, single buildings) have no ZCTA. Where Zillow publishes no ZIP-level value — mostly rural areas — the county color shows through instead of a no-data shape. ZIP values are refreshed by the same daily job as the counties.
FIPS handling
Connecticut: Zillow and the Census may publish either the legacy eight counties or the 2022 planning regions. The map shows whichever set the current dataset uses and hides the other. Alaska boroughs and census areas follow the 2020 boundaries; historical boundary changes may leave some areas without data.
Geography
Census 2020 cartographic boundary files, simplified, in an Albers USA composite projection with Alaska and Hawaii insets.
Data refresh
A daily automated job checks Zillow's file, validates it, keeps the previous valid dataset if anything fails, and publishes only when a new month appears. Last successful update: —.
Per-metric reference
| Metric | Source | Observation date | Coverage | Calculation | Seasonally adjusted? | Missing-data treatment | Last successful update |
|---|---|---|---|---|---|---|---|
| Typical home value (ZHVI) | Zillow Research ZHVI, all homes, county | Month-end, monthly | U.S. counties with ZHVI coverage | Published value | Yes (smoothed, SA) | Shown as No data | — |
| % change (1M–10Y) | Derived from ZHVI | Latest month | Counties with both endpoints | (V_t / V_{t−h} − 1) × 100 | Inherits ZHVI | Unavailable if either month missing | — |
| Annualized change | Derived from ZHVI | Latest month | Horizons > 12M | ((1+c)^(12/h) − 1) × 100 | Inherits ZHVI | Unavailable | — |
| Inflection signal | Derived from ZHVI | Each month | Counties with ≥ 15 months | Rules A–F below | Inherits ZHVI | No signal | — |
| Population | Census Vintage 2020 estimates | Jul 1, 2020 | All counties | Published value | n/a | Shown as — | — |