What Is ZHVI? The Zillow Home Value Index, Explained
Every forecast on Sialim is built on ZHVI. This guide covers what the index measures, how it differs from the median sale price, and where it can mislead you.
The one-sentence version
The Zillow Home Value Index (ZHVI) estimates the value of the typical home in a market each month, whether or not that home sold.
What ZHVI measures
Zillow computes an estimated value for nearly every home in the United States, then aggregates those estimates into an index for each geography it tracks: nation, state, metro, county, city, and ZIP code. The headline number you see quoted, and the one Sialim forecasts, is the mid-market cut: all home types (single-family plus condo), middle tier, smoothed, seasonally adjusted.
Each of those qualifiers changes what you are looking at:
Middle tier means homes between the 33rd and 67th percentile of value in that market. A metro's ZHVI of $450,000 says a typical home there is worth about that much. Luxury and entry-level segments get their own tiers.
Smoothed means each month's value averages in recent months, which removes noise from the estimation process.
Seasonally adjusted means the predictable spring bump and winter lull are stripped out. When a seasonally adjusted series rises, the market strengthened beyond the normal calendar pattern.
ZHVI vs. median sale price
The median sale price only counts homes that sold. That sample changes every month: if buyers shift toward cheaper homes because rates rose, the median falls even when no individual home lost value. Economists call this mix shift, and it makes sale-price medians jerky and easy to misread.
ZHVI sidesteps the problem by estimating all homes, sold or not. The cost is that it depends on Zillow's valuation model rather than recorded transactions. In practice the two series tell the same story over quarters and years, but ZHVI tells it with far less month-to-month noise, which is why we model it rather than sale prices.
ZHVI vs. Case-Shiller
The S&P CoreLogic Case-Shiller index uses repeat sales of the same homes, which makes it the academic gold standard for measuring pure price change. Its drawbacks are coverage and speed: it tracks 20 metros against ZHVI's roughly 900, and it publishes with a two-month lag as a three-month moving average. If you want to compare Boise to Buffalo this month, Case-Shiller cannot help you. ZHVI can.
Where ZHVI can mislead you
It is a model output. Zillow revises past values as its estimates improve, so the history you download today differs slightly from last year's file.
Smoothing hides turning points. A smoothed, averaged index reacts to a sudden market break a month or two late. In fast markets, inventory and days-on-market data turn first.
Low-volume markets estimate poorly. In small metros with few transactions, the model has little to learn from, and values move in odd steps. Treat small-metro ZHVI, and any forecast built on it, with wider error bars. Our own accuracy numbers on each metro page reflect this.
How Sialim uses ZHVI
We fit a separate forecasting model to each metro's ZHVI history, add mortgage rates, inventory, and labor data where they help, and publish next-month forecasts with backtested accuracy for every metro Zillow tracks. The full recipe is on the methodology page; the results are on the opportunity map and rankings.
Frequently asked questions
Is ZHVI the same as the median sale price?
No. Median sale price describes only the homes that sold in a given month, so it jumps around when the mix of sold homes shifts. ZHVI estimates the value of all homes in a market, including the ones that did not sell, which makes it steadier and better for tracking trends.
What does the "middle tier" in ZHVI mean?
Zillow publishes ZHVI in tiers. The middle tier covers homes between the 33rd and 67th percentile of value in that market, which is the standard cut for a "typical" home. Top-tier and bottom-tier versions track the expensive and cheap ends separately.
How often does ZHVI update?
Monthly. Zillow publishes new values around the middle of the following month, at national, state, metro, county, city, and ZIP code levels.
Can I use ZHVI to value my own home?
No. ZHVI describes a market, not an address. For a single property, Zillow's Zestimate is the per-home product, and a local appraisal beats both.
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ZHVI data © Zillow, via Zillow Research. Zillow publishes full technical documentation of the index methodology there.