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Real Estate Market Reports FAQ

Zillow Data Frequently Asked Questions and Metric Definitions

Zillow analysts regularly calculate information from more than 350 metro areas across the country on home values, listings data and equity information, to name a few. The process of calculating so much data is complex, and questions about methodology are common.

Q. Where do you obtain your data?

A. Our data on and appreciation for these reports is based on the Zillow Home Value Index - a valuation index calculated as the median value (Zestimate) of all homes in a particular geographic area. At the national level, this data is then weighted according to population in each area.

Loan equity data is derived from public records - loan amounts that are typically recorded in each county and publicly available through a county recorder's office.  We cross-reference this public data with valuations on millions of individual homes then calculate the median owner equity for a geographic area.

Foreclosure transactions are derived from public data and are representative of foreclosed homes possessed by a bank in Q1.

Q. What is the Zillow Home Value Index and how is it calculated?


A. The Zillow Home Value Index is the median value of all homes in a geographic area. It is a valuation index calculated as the median value (Zestimate) of all homes in a particular geographic area. At the national level, this data is then weighted according to population in each area.

Q. What is the difference between median and average, and why do you use median?

A. The median is the midpoint in a list of numbers. An average is the total amount of list divided by the number of numbers. Median is a more accurate measure because it removes outliers - data that is far above or far below what is common in an area.

For example:

There are only seven homes home sales in the past year in ZIP code 'x.' Most homes in the area are of similar size - between two and three bedrooms. But during the past year, one much larger home on a 100-acre lot also sold. These are the sale prices:

$275,000
$300,000
$300,000
$350,000
$375,000
$375,000
$1,800,000

If we were to look at the AVERAGE sale price in 'x' based off of these sales, it would be $539,285. That value is not representative of any of the homes in the ZIP code.

If we were to look at the MEDIAN sale price in 'x' based off of these sales, it would be $350,000 - a more accurate representation of the majority of homes in the area.

Q. How often is this data updated?


A. The data is updated weekly.

Q. Can I republish this data?


A. You are welcome to republish any of this data as long as you attribute it to Zillow.com.  In fact, you can download an Excel spreadsheet from any page for your use - see "download full report" and "download chart data" on the lefthand side of any local market trend page. If you are publishing online, please also include a link to the local market trend page where you obtained the data.

Q. How can I ask questions about this data?

A. The best place to ask questions about real estate data is within Zillow Advice. Here you can have your questions answered from a variety of sources, including Zillow representatives and real estate professionals in your area.

If you have questions about republishing data for your publication or blog, please contact Zillow Communications at press@zillow.com.

Q. Why isn't my location available?

A. Occasionally we are not able to obtain enough data to provide an accurate snapshot of what is happening in a particular area over a particular period of time. For example, in some nondisclosure states, where home sale transactions are not a part of public record, we are often not able to calculate reports. When that's the case, we remove those numbers.

Q. Why does the data in the graph have gaps in it?

A. Typically gaps in data on the graphs occur because we have yet to meet our threshold of data required to calculate accurate findings about a particular geography. However, we do update the data each week so while the data point may not be there one week, it could very well be there the next, if we receive more data for the area or particular time period.

Q. Why is the graph I am looking at so jagged?

A.  Data in smaller geographical areas, such as a ZIP code or neighborhood, has the potential to be more volatile due to fewer representative homes and transactions.  When looking at these statistics to determine housing trends for a particular area, it is more reliable to look at year-over-year statistics versus a shorter period like month-over-month, as tracking over an extended period of time allows for a better understanding of trends and eliminates seasonal variables.

Q. Why do you have data for one time frame (MoM, QoQ and YoY) but not another?

A. Typically data is unavailable in a particular time frame because we currently do not have enough data in either the preceding or current time point to calculate. We do update the data each week so while the data point may not be there one week, it could very well be there the next.

Q. What time period is covered in the data?

A.  The data is a compilation of all data up until the date listed on the time stamp just under the table. As we receive additional data for the time period prior to the date stamp, it is added weekly.

Q. Why did you have data for my ZIP code/city/metro area in the past but now it is gone?


A. To report on new data we must reach a threshold of accuracy to report on the data point. If the threshold has not been met, we will not report on the data until it has. If there is insufficient data for us to calculate current statistics, we will leave them blank. If the data was there before, it was because we had more data for the past time period. We do update the site every week, however, and if we receive more data, we will add the statistics back to the site.


Q. What is the difference between 'Homes Foreclosed' and 'Foreclosure Re-sales'?

A. 'Homes Foreclosed' is when the home owner surrenders ownership, and this can happen in two ways. It can occur when the home is forfeited by the homeowner to the bank or, in the case of a Sherriff's Sale, when a third party buys the home at an on-site or courthouse auction.
The Foreclosure Re-sales metric captures mostly sales of bank-owned homes. These are the transactions in which the bank sells the home within one year of the home's foreclosure date. Foreclosure Re-sales also capture the less common situation in which the third party who bought the home at a Sherriff's Sale is the seller.

Q. Are foreclosures included in the Zillow Home Value Index?

A. No, foreclosures (when a homeowner loses their home to a lender) are excluded. We also exclude the sales of REOs (real estate owned by banks). These homes, with the bank as the seller, often sell for a lower price than a typical home.

Q. Why don't you include foreclosures in the Zillow Home Value Index?   

A. Our data is meant to give a general indication of the value of their home were they to sell it on the open market, not have it foreclosed upon. If we combined both foreclosures and non-foreclosures into a single metric, we don't believe we'd provide good insight into either market.

In many areas today, if you include foreclosures in a single metric, you're underestimating the decline in value of foreclosed homes and overestimating the decline in value of non-foreclosure homes.

However, since foreclosures exert downward pressure on the prices of non-foreclosure homes nearby, and those sales prices are included when we factor our Zestimates, the influence of foreclosures can be seen in our data.

Check out our blog post on the influence of foreclosures on home value indexes.

Metric Definitions

Zillow Home Value Index (ZHVI):

  • Median (mid-point) of all Zestimates in a geographic region. Half of the Zestimates are above this number and half are below it.
  • Reported monthly and compiled from data dating back to 1996. The historical Zillow Home Value Index is re-computed twice a month.
List price ($):
  • Median (mid-point) of the listing price of all homes during the reporting period. This includes listings that have been in the Zillow database for at least one day.
  • Reported monthly and compiled from data dating back to October 1, 2008.
Sale price ($):
  • The median sale price of all homes (including foreclosed homes) in a given geography. Half the homes sold above this number and half sold below.
  • Reported monthly and compiled from data dating back to 1996. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest). The historical median sold price is re-computed twice a month.
Days listed on Zillow:
  • Median (mid-point) number of days for-sale homes in a given geography are listed on Zillow. To be included in this data point, a home must have been listed for sale on Zillow for at least one day during the reporting period.
  • Reported monthly and compiled from data dating back to October 1, 2008.
Homes for sale on Zillow:
  • The number of homes appearing in the Zillow listing database for at least one day during the reporting period. This includes 'For Sale by Owner' and foreclosure listings.
  • Reported monthly and compiled from data dating back to October 1, 2008. The historical homes-for-sale data point is re-computed twice a month.

Total homes sold:
  • The number of homes sold in a given geography.
  • Reported monthly and compiled from data dating back to 1996. The historical number of homes sold is re-computed twice a month. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest).

Value per Square Foot ($):
  • Individual values per square foot are computed by dividing the home's Zestimate by the square footage. This metric measures the median (mid-point) of all these values in a given geography.
  • Reported monthly and compiled from data dating back to 1996. The historical value per square foot is re-computed twice a month.
List price per square foot ($):
  • Median (mid-point) price per square foot for all listed homes in a given geography (individual price per square foot is computed by dividing the latest listing price of a home by the square footage).
  • Reported monthly and compiled from data dating back to October 1, 2008.
Sale price per square foot ($):
  • Sold price per square foot for individual homes is computed by dividing the home's sale price by the square footage. This metric measures the median.
  • Reported monthly and compiled from data dating back to 1996. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest). The historical median sold price per square foot is re-computed twice a month.
List-to-sale price ratio:
  • The median (mid-point) of the ratio between the list price at the time of the transaction and the final sale price of the home for all Zillow listings which have sold in a given geography.
  • Reported monthly and compiled from data dating back to October 1, 2008. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest). The historical median list-to-sale price ratio is re-computed twice a month.
Listings with price cut (%):
  • The percent of all for-sale home listings in a given geography that currently have a reduced price from the maximum listing price of the three preceding months.
  • Reported monthly and compiled from data dating back to October 1, 2008. The historical percent of homes with price reductions is re-computed twice a month.
Amount of price cut (%):
  • The median (mid-point) percentage of all reductions in the listing price of for-sale homes in the reporting period for a given area. Based on for-sale listings on Zillow.
  • Reported monthly and compiled from data dating back to October 1, 2008. The historical median percent of price reduction is re-computed twice a month.
Sold for loss (%):
  • The percentage of homes in a given geography that sold for less than the previous purchase price. This excludes foreclosed homes and sales and the consecutive sale of the foreclosed home.
  • Reported monthly and compiled from data dating back to 1996. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest). The historical percent of homes sold for a loss is re-computed twice a month.

Sold for gain(%):

  • The percentage of homes in a given geography that sold for more than the previous purchase price. This excludes foreclosed homes and sales that occur within a year of a foreclosure (i.e. , sales of bank-owned homes).
  • Reported monthly and compiled from data dating back to 1996. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest). The historical percent of homes sold for a gain is re-computed twice a month.

Homes foreclosed (%):

  • The percentage of all homes in a given geography that have been foreclosed on in a given month. A foreclosure is when a homeowner loses their home to their lending institution or if it is sold to a third party at an auction.
  • Reported monthly and compiled from data dating back to 2000. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest). The historical percent of homes foreclosed is re-computed twice a month.

Foreclosure re-sales (%):

  • The percentage of sales in a given geography that were foreclosure re-sales (a sale of a home that occurred within 12 months after the home was foreclosed). This metric captures mostly bank-owned sales.
  • Reported monthly and compiled from data dating back to 2000. Each data point is a weighted average of the value in the prior three months (with the most recent month weighted highest). The historical percent of foreclosure re-sales is re-computed twice a month.

Increasing values (%):

  • The percentage of all homes in a given geography that have increased in value in the past 12 months (current Zestimate is higher than Zestimate 12 months ago).
  • Reported monthly and compiled from data dating back to 1996. The historical percent of homes with decreasing values is re-computed twice a month.

Decreasing values (%):

  • The percentage of all homes in a given geography that have decreased in value in the past 12 months (current Zestimate is lower than Zestimate 12 months ago).
  • Reported monthly and compiled from data dating back to 1996. The historical percent of homes with decreasing values is re-computed twice a month.

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