Zillow Announces Zestimate Improvements

Starting this evening, we have expanded and improved our database of nearly all homes in the U.S., adding more data on more homes and improving the accuracy of our proprietary Zestimate® home valuations.

Read more about this exciting change in our Zestimate Improvements FAQ.

We understand that there may be many questions about specific Zestimates. As our Zestimate algorithm is proprietary we will be unable to answer with specificity why your Zestimate is what it is, or why it may have changed with these improvements. Again, we invite you to read our FAQs on the topic to get a better understanding of what Zestimates are all about:

Zestimate Improvements FAQ
What is a Zestimate?

We will also be updating our Zestimate Values and Accuracy data.

Update: We now have two blog posts on the recent changes...

Zillow Expands and Improves Database of Homes
Upgrading the Zestimate

Thanks for using Zillow!
Russ
Zillow Customer Support and Community Relations
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June 13 2011 - US
We think we've answered this question for you!
 
 

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Profile picture for wetdawgs
bumping
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June 19 2011
Profile picture for High1771
Another concerning thing re: the new algorithm is when I look at homes for sale in my neighborhood.  Depending on the square footage, you'll see asking prices anywhere from 320k to 500k.  Right below each is a Zestimate, and the Zestimate is consistently about 100k (or more) below the asking price.

While asking prices may not be exactly on the ball, they are not going to be off by anywhere near that discrepancy.  No agent in their right mind would let that happen.

My point is not to add further fuel to the fire that the Zestimates have some work to do... it's to point out that in the data team's due diligence, these are things they should be looking at.  It's a ten line SQL query to look for anomalies like this.  You have whole neighborhoods where the Zestimate is no longer in the ballpark of what agents and sellers believe the houses to be worth.  Are they wrong, or is the algorithm?  Not a very tough call, in my opinion.

Again, not saying the Zestimates should exactly match - in these times, sellers are probably still asking too high.  But not by these margins.  Not even close.  If I were about to release a new product, these would be giant red flags to me.
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June 19 2011
Profile picture for dinobino
Something is wrong with the new zestimates, end of story. According to my "new and improved" history my house was worth 158k in August 2010 and then in Sept 2010, one month later, it was worth 123k, then the very next month it was worth 158k again, and now it is worth 115k. WRONG.

My house is worth approximately 135k and I guarantee it has not been valued at 158k in the past year. It's been apprasied at 150k, but I know due to the market I can't expect that.

Not sure I can ever trust Zillow again.
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June 19 2011
Profile picture for julapnet
Why would zillow go and change historical estimates. Any person with half the brain knows that you should no change historical charts. Time to speak out and discredit this site.
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June 19 2011
Regarding historical estimates:

With the change in the algorithm, we also re-estimated historical Zestimates so that our previous house-level trends would be more accurate as well. Some users often think of historical Zestimates along the lines of a stock price which cannot change in value historically (i.e., once the market closes, the closing price is fixed and will always be what it was on that day).  Historical stock prices are different than historical Zestimates, however, because the former are facts (and thus can't change), whereas the latter are estimates and, as such, can change when superior approaches are developed to estimate the value historically.
 
Importantly though, we always estimate historical values using only the information available at that time of that estimate so we would not, for example, use a future sale price to estimate a home value at a prior point in time.
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June 19 2011
Profile picture for Dunes....
Hicbump!
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June 19 2011
Dear Rachel Rosen,

Really!!!  

"... we also re-estimated historical Zestimates so that our previous house-level trends would be more accurate as well ..."   

Really!  Zillow's historical estimates are a direct measure of its performance. By changing the past estimate reports, you are not only rewriting history but you are also rewriting Zillow's performance.   
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June 20 2011
Profile picture for brownepj99
I knew something had happened, and I was not happy! My house had been tracking at $297K with accurate graph for the last two or more years. Then all of a sudden it was valued at $251K, AND, the graph makes it look like it was always that low! Rediculous! Also, the lower value does not track recent sales well in my neighborhodd, in terms of simple $ per square foot, or similar sales. Zillow, this new algorithm is WRONG, and UNFAIR!
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June 20 2011
Profile picture for supercodydog
Almost all economic time series data gets revised as new info comes in. I dont really see the big deal. If Zuesstimates had jumped 10%, I wonder if all these posters would be self-congratulating and not berating Zillow.

Maybe Zillow should make the old data for sale or available in some downloadable format if people want to track old v new.

Or maybe some want to have a benchmark to say, eg, my house value is x% above Zillow to argue for higher prices. .

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June 20 2011
Profile picture for northwest
No doubt we would all be happy if our properties had all jumped 10%. Would we have believed it? No, it is unrealistic. Many of us see weird abnormalities as a result of the new algorythm and history calculations which do not seem realistic either. We have come to rely on Zillow as the best tool out there or we wouldn't care. We look to them to be responsible and responsive, and are pointing out what we think needs correction. 
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June 20 2011
Profile picture for allier123
My May Zestimate stated my home's value decreased 2.7% to $266500 from $273500, but this month's Zestimate states the value "increased" 2.3% to $192500. What gives? That's a $74000 decrease instead of an increase! The values for my neighborhood have always been above $220000 and I purchased mine at $253900 in 2006. Something happened with this month's data. 
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June 20 2011
Profile picture for tblonghorn
The new algorithm appears to be total crap.  Zillow was already undervaluing the homes in my neighborhood compared to every other estimate I can find.  The new algorithm dropped those (already low) values by an additional 30-40%!

I live in Dallas where the market has not cratered like many other metropolitan areas, yet Zillow shows a 50% decrease in values from just 2007 (after prices were already on the decline) under the new algorithm.  Additionally, using the old algorithm in 2006 and the new algorithm today, the site shows a 67% decrease in price in a market that doesn't reflect that sort of drop.

This brings into question the validity of any estimate provided through this website since its inception.  It seems like it is time to look to other sources.
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June 20 2011
Profile picture for pjv22
my home dropped from $565,000 to $498,000 when you changed your algorithm ,ad the house next to mine just sold for $550,000.
this is ridiclous
i will no longer use Zillow and will email all my adress contacts how bizarre your site has become.
PS i just had appraisal at $ 575,000
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June 20 2011
Profile picture for jaydarg

Zillow raised the value of my home $140,000 from last month with an estimate dated 6/15.  Then I refreshed the page and the value went down $220,000 (from 6/15 to 6/17).  Whatever credibility you had went out the window.  A home 3 doors down with 900 less sq. feet and 5 to 10 year older is estimated at $70 k more than mine.........I can go on and on.  I would love it if I could use these values for my tax assessment, but they just laugh.  When I talk to a realtor, he estimates the property value at at least $400 k more than the what Zillow valued the property on 6/17.  This estimate is worse than what you had before.  I live in the Houston TX area.

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June 20 2011
Profile picture for knga
Three points: Do changes reflect tax assessments?  Will prices correct over time?  Does Zestimate matter...well, get it in writing.  Zestimate and tax assessments: In my area -- Bethesda MD -- tax assessments have been fluctuating wildly, creating big disparities among neighboring properties and subsequent re-assessments.  First, towns sought to cash-in on rising values with graduated increases -- which created a backlash once market plunged.  If alogithm takes taxes into account then it will reflect current chaos.  This might all correct by years' end if the sales of comparables show Zestimates to be wacky.  Of course, Zestimate may be a factor in buyers' perception of value in which case it becomes self-fulfilling, which would be too bad.  Does Zestimate affect value?  It's an empirical question.  Here's what to do:  Get any reference to Zestimate from loan officer, potential buyer, real estate agent, or appraiser IN WRITING. 
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June 20 2011
Profile picture for Dunes....
Bump back to the 1st Page where this Belongs...
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June 20 2011
Profile picture for xtacles
I agree the new formula is far from correct. Zillow is no longer helpful at all- to people personally or for work (I used it for insurance purposes). Massive value drops, then showing that is what the home has always been worth? Ridiculous. I just had my home appraised and Zillow is $100,000 off.
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June 20 2011
@ pjv22 @tblonghorn et al 
send me your address and we'll take a look. need house#/street/city/state/zip
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June 20 2011
Profile picture for rugbythedog
My house price jumped up about $50K from last month (though Zillow says it has gone down $36K).  Many houses in my neighborhood are over $100K higher than they were just last month on Zillow.  Not complaining as my house now shows as more valuable in case I want to sell, but it does raise more doubts about Zillow's estimates, accuracy, and value.
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June 20 2011
Profile picture for Dunes....
Bump back where this Belongs...Front Page
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June 20 2011
Profile picture for TerryHershner
Rachael, can we get access to the old zestimate data?  For at least a while now, it looks like that may be a little more reliable to us as it didn't have these massive back and forth 200% spikes we are seeing on so many properties.  Since it may be a few months until all these issues, we can at lease use it as a guide to help make a decision if we feel the new data is way out of whack.  One I looked at today near my neighborhood went from $180k sometime in early June when I saw it to $280k today where everything around it is falling.  The tax value just went from $165k to $141k.  So it is 100% higher than the tax value.  That's a little hard to swallow.  I'm thinking that until the new algorithm works the bugs out, most of us felt the old method was overall more reliable.  The new algorithm may on average be 4% better (12% error to 8%) but it has caused many individual properties to be in excess of 100% off and it makes it very difficult to trust it when there are obviously errors which can not be explained.  Thanks.
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June 20 2011
Profile picture for supercodydog
I dont really disagree with Zillow's estimates all that much. I think that many owners price off each other and when nothing sells, they are all thinking their market is stable when , in reality, the difference between bid and offer is so large that there are no transactions clearing.

It would be interesting in the 100million estimates zillow has, if they could put out some easy stats, like how many went down, or up and by how much and if possible, in what sort of increments. And of course by state or zip code.

That could help with better understandings.
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June 20 2011
Profile picture for Dunes....
Back I say..back to the 1st page

Bump
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June 20 2011
Profile picture for zinck74
This has become a joke.  My condo is currently "zestimated" at $70K less than pretty much the exact same condo one floor above me.  Exact same floor plan and everything.  This represents a 30% difference.  (!!)  Ridiculous.  What's even the point of coming here any more?
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June 20 2011
Profile picture for AOTW
  • AOTW
  • Contributions:35
It's still "garbage in, garbage out".
Compare this:
http://www.zillow.com/homedetails/3110-Woodside-Rd-Woodside-CA-94062/15597056_zpid/#{scid=hdp-site-map-bubble-address}

With real world info:
http://www.sawbuck.com/property/Bay_Area/94062/Woodside/8063315-3110-Woodside-Road
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June 20 2011
Profile picture for hpvanc
The new algorithm seems to generate Zestimates for homes that do not have public records, while this may be ok for homes that have been entered and cannot be tied to a public record, it is creating a major problem in too many cases.  Lot's of complaints that on the forums that my house has 2, 3 or more Zestimates, how do I delete all but the highest one.  Unfortunately the highest one may not be the most accurate, hopefully the one tied to the public records is the most accurate, either way their will owners and buyers will have issues with these duplicate Zestimates.
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June 20 2011
Profile picture for tls100309
Zillow has lost all credibility in my mind.  There is  no way my property has decreased by 49% in the past year and a half.  Especially since I've put $30,000 dollars worth of work into it!  Seems like they need to find a new statistician!!!
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June 21 2011
Profile picture for allier123
Zillow is ignoring the facts that I have submitted regarding my house and the homes in my subdivision. The public record is accurate and does not need to be re-written. I am just the second owner of this property since 1993 and the tax assessment only changed upwards significantly when I bought it from the original owners. There is no valid reason to restate history if you are not going to use what is already written as public knowledge. The new historically restated Zestimate is below the tax assessd value of the original owners in 2006 before we bought it. You all have written your own version of what was 100% accurate because it told what actually happened. Your new version devalues the properties in our subdivision and hurts those who have homes on the market at significantly higher prices than your Zestimate. If this continues I'm sure our Mayor and Metro Council may soon get involved in this discussion as it impacts this entire city.
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June 21 2011
Profile picture for prairiestyle

Zillow's new release dropped Zestimates on my street by 70%. My own home ( listed here: http://www.zillow.com/homedetails/2517-Cherokee-Pkwy-Louisville-KY-40204/73455025_zpid/) lost almost $700,000 overnight. As mistakes go this is fairly dramatic. 

Zillow's own--also recently updated--accuracy data tables demonstrate the depth of the problem. I am located in Louisville, the biggest city in Kentucky. The county is Jefferson County. Tracking through the "Data Coverage and Zestimate Accuracy Tables" to Kentucky and then to Jefferson County http://www.zillow.com/howto/DataCoverageZestimateAccuracyKY.htm
 brings up the problem. The table indicates no stars for the county (meaning no valuation data), and notes there are no homes in Jefferson County with Zestimates--something demonstrably in error.

This new release is internally inconsistent and deeply wrong. The local real estate community is concerned as they have appreciated Zillow's efforts to date. I hope this is ironed out soon,  Not only is this new release not a reflection of the current local market, where houses are actually selling for close to their previous  "un-updated" Zestimates, but it appears to be troubled and buggy.
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June 21 2011
Profile picture for tls100309
WOW prairiestyle!!!  That is just down right ridiculous!  They really need to get it together!  At least your historic value shows 1.2M.  Mine doesn't even show what it was last week at $47,000 higher.  I'm not sure what is going on, but it is very outrageous!  
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June 21 2011
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