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Zestimate Improvements

On June 13, 2011, we made some improvements to the Zestimate home valuations algorithm that may have impacted your home's Zestimate. Here are some frequently asked questions to explain the changes.

What kinds of Zestimate improvements did you make?
Simply, we expanded and improved our database of nearly all homes in the U.S. by adding more data on more homes and improving the accuracy of our proprietary Zestimate® home valuations.

How did you "expand" the database?

We added Zestimates to more than 25 million new homes, bringing the number of homes on Zillow with data, Zestimates and Rent Zestimates to approximately 110 million*. That's more than three-quarters of all homes in the country.

What kinds of improvements did you make to the Zestimate?

We improved the algorithm models that better incorporate user-submitted data and market data. This has improved the Zestimate median margin of error to 8.5 percent nationwide. Previously, it was 12.7 percent.

What do you mean by user-submitted data?
Zillow users have made updates on more than 28 million homes, adding information such as remodel and home fact information that's not reflected in public records. These updates are used to calculate more accurate Zestimates on more homes.

What user-submitted facts can affect the Zestimate?
Updating facts like the number of bedrooms and bathrooms in your home, or the square footage, may affect your Zestimate.

How much did my home's Zestimate change?
That depends on many factors, like where you live and how much information we have on your home. Most likely, the dollar amount on your home changed. But month-to-month changes you might see will be indicative of what's happening in the market -- not due to changes in our algorithm.

How often are Zestimates for homes updated?
We refresh Zestimates for all homes three times a week.

How do you measure Zestimate accuracy?
We test Zestimate accuracy by measuring individual home Zestimates against actual sale prices. See more about Zillow Data Coverage and Zestimate Accuracy.

Where did you add Zestimates?

Homes in states like Iowa, West Virginia and New Hampshire will now have many more homes with Zestimates than they did previously.

My home still doesn't have a Zestimate. Why not?
Even though we added 25 million more homes with Zestimates, there are still some states or municipalities where accessing information about homes and transactions is very difficult. We do not have enough data to publish Zestimates in those areas.

Will these changes impact the Zestimate history?
Possibly. We've applied algorithm changes to the history going back to 2006,  but we are not sure if everyone's Zestimate history changed with these improvements. These improvements were important to do because we want changes in Zestimate values over time to reflect changes in the market, not changes in how Zillow computes its algorithm. Our new algorithm doesn't just improve current accuracy; it improves historical accuracy, giving consumers a better idea of what a home was worth over time. We are now working on re-doing all the history.

What if I think my Zestimate isn't right?
You can do a few things:
  • Update your home facts. Correcting home facts could affect the Zestimate.
  • Enter an owner comment. On each home details page is a section for "Owner Comment." This is a place where owners can explain why they think their Zestimate is too high, too low or just right. For example, suppose you just renovated your home. You can add that information and update your home's estimate there.
  • Report a problem. If the county record information is wrong, use the "Report problem" link under "Edit" on the home details page. We will contact the data provider and ask them to check that information in the county records.
I see that the "My Estimate" tool is now gone. Is that change related to the Zestimate improvements?
We are doing some work to improve the "My Estimate" tool and hope to have it back up soon. In the meantime, homeowners can and should continue to update their home facts. Some home facts can directly affect the home's Zestimate.

I spent a lot of time creating a "My Estimate" for my home. Will it now disappear?
No, it will remain as-is for the time being. However, if you attempt to edit it further, the tool will not work. We are doing some work to improve the "My Estimate" tool and hope to have it back up soon.

* Google Analytics - March 2013

By Diane Tuman
Saving changes
  • Last edited April 04 2013

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