What is a Zestimate?



The Zestimate (pronounced ZEST-ti-met, rhymes with estimate) home valuation is Zillow's estimated market value, computed using a proprietary formula. It is not an appraisal. It is a starting point in determining a home's value. The Zestimate is calculated from public and user submitted data; your real estate agent or appraiser physically inspects the home and takes special features, location and market conditions into account. We encourage buyers, sellers and homeowners to supplement Zillow's information by doing other research such as:

    Getting a Comparative Market Analysis (CMA) from a real estate agent
    Getting an appraisal from a professional appraiser
    Visiting the house (whenever possible)


What's the Value Range?

The Value Range, which is related to the Zestimate, shows the high and low estimated values of a home (e.g., the Zestimate may be $260,503, while the Value Range is $226,638 -- $307,394). The Value Range can vary in magnitude depending on our historical ability to estimate similar homes. A wider range indicates less data is available or there is more volatility in the data. A smaller value range means we have lots of information to help compute the Zestimate and Value Range. When thinking about a Zestimate for a home, we believe it is critical to
consider the width of the Value Range for that Zestimate as this is giving you an important clue as to the anticipated accuracy of the Zestimate. For the statistically minded, the Value Range is actually a 70 percent confidence interval.

My Zestimate is too low - or too high. What gives?

As mentioned previously, the Zestimate is a starting point in figuring out the true value of a house  The amount of data we have for the house affects the Zestimate accuracy. If your home facts are incorrect or missing, you can update your facts, which may affect your Zestimate value.

  • Price history and tax history: Check to see if your price history (the sale price and date you bought your home) and your tax history are correct on Zillow. Depending on the area in which you live, this can be a big factor in your Zestimate. If data is missing or incorrect, please let us know. Click "Edit" on your home details page, then "Report Problem With Home."

Updates and remodeling explained: Most upgrade information is not in the public records and is not easily quantifiable. We do not know about home updates and remodels unless they have been reported to the local tax assessor, so those items are not used in Zestimate calculations. While we do utilize user-submitted data that is measurable, (e.g., additional bedroom count, bath count and square footage) there is no way for us to systematically gather and verify the type of remodel or build information where the value is based upon how the
final product appeals to the buyer. Because of this, the algorithm can't use that information.

Your home icon on the map: Region boundaries usually do not affect the Zestimate. That being said, if the home icon is in the wrong spot, either Zillow staff or the homeowner can correct that. Move Home Instructions

I just changed the home facts. When will my Zestimate update?

Updates to your home facts will be factored into your home's Zestimate, but, if the updates are not significant enough to impact the home's value, your Zestimate may not change. In some cases, the altered data will affect the estimates slowly over about a two-month time period.  You will not see the full impact of the revision during the next estimate cycle. We refresh Zestimates for all homes three times a week. On rare occasions, this schedule is interrupted by operations associated with algorithmic changes or the deployment of new analytic features.

How does the amount of data affect it?

The number of transactions in a geographic area affects how much we know about prevailing market values of homes in that area. More transactions provide more data and improve the accuracy of the Zestimate. Also, we use public and user-provided data for house attributes, and some areas report more data than others. The more attributes we know about homes in an area (including yours), the better the Zestimate. Remember that homeowners can also update their home facts if they feel they are incorrect or there are missing values, and the updates may affect the Zestimate value.

Is a Zestimate an appraisal?

No. The Zestimate is not an appraisal, and you won't be able to use it in place of an appraisal, though you can certainly share it with real estate professionals. It is a computer-generated estimate of the worth of a house today, given the available data. Zillow does not offer the Zestimate as the basis of any specific real estate-related financial transaction. Our data sources may be incomplete or incorrect; also, we have not physically inspected a specific home. Remember, the Zestimate is a starting point and does not consider all the market intricacies that can determine the actual price a house will sell for.

How do we come up with the Zestimate and what's in the formula?

We use proprietary automated valuation models that apply advanced algorithms to analyze our data to identify relationships within a specific geographic area, between this home-related data and actual sales prices. Home characteristics, such as square footage, location or the number of bathrooms, are given different weights according to their influence on home sale prices in each specific geography over a specific period of time, resulting in a set of valuation rules, or models that are applied to generate each home's Zestimate. Specifically, some of the data we use in this algorithm include:

Physical attributes:    Location, lot size, square footage, number of bedrooms and bathrooms and many other details.
Tax assessments:     Property tax information, actual property taxes paid, exceptions to tax assessments and other information provided in the tax assessors' records.
Prior and current transactions:     Actual sale prices over time of the home itself and comparable recent sales of nearby homes.

Currently, we have data, Zestimates and Rent Zestimates on approximately 100 million homes on Zillow.*

Why do I see home values for the past?

We not only have Zestimates for homes now, we have used massive computing cycles to go back in time to generate historic Zestimates as well. Sound hard? It is, but it's critical because it allows you to see how a home (or an area) has changed in value over the years.

Do you ever change prior Zestimates?

Yes. When major improvements to the algorithm are made, we do re-compute the historical Zestimates for affected homes. Our purpose in doing so is to provide consumers with the best estimate of historical property valuations. A historical Zestimate is not like a historical stock price, which doesn't change after being recorded. A stock price is a record of an actual empirical event (and, as such, shouldn't change).

A Zestimate, on the other hand, is an estimate of the market value of a home, and can change when we have a better algorithm to estimate that value.

Note: We never allow future information to influence a historical Zestimate (for example, allowing a sale in 2009 to influence a Zestimate in 2008). Each historical Zestimate only uses information (e.g., prior sales, tax assessments) known prior to the date of a given Zestimate.

Does the Zestimate algorithm ever change?

Yes, a team of statisticians working every day to make the Zestimate more accurate. Since Zillow's inception in 2006, we have deployed three completely new versions of the algorithm (2006, 2008 and 2011), but incremental improvements are made between major upgrades with new iterations being deployed regularly.

How often are Zestimates for homes updated?

We refresh Zestimates for all homes three times a week. On rare occasions, this schedule is interrupted by operations associated with algorithmic changes or the deployment of new analytic features



Are foreclosure sales included in the Zestimate algorithm?

No, the Zestimate is intended to provide an estimate of the price that a home would fetch if sold in a full-value, arms-length sale (e.g., the sale isn't for partial ownership of the property or between family members). Our extensive analysis of foreclosure re-sales (typically, but not always, real estate owned, or REO, sales) supports the conclusion that these sales are generally made at substantial discounts to comparable non-foreclosure sales. As such, these sales are not used by the algorithm to produce the Zestimate. That is not to say that foreclosure re-sales do not influence the Zestimate at all, as foreclosure re-sales do suppress the sale price of surrounding non-foreclosure homes, and the price signals from these surrounding homes are used by the algorithm to produce Zestimates in that area.

Who calculates the Zestimate, and how do they do it?

The Zestimate is created by an automated software process, designed by statisticians, and there is no ability for humans to manually alter the Zestimate for a specific property.

Does Zillow delete Zestimates? Can I get my Zestimate reviewed if I believe there are errors?

We do not delete Zestimates. We monitor customer feedback for systematic issues with the algorithm, but do not change individual Zestimates in response to customer feedback. The Zestimate is designed to be a neutral, unbiased estimate of the fair market value of a  home, based on publicly available and user-submitted data. For this purpose, it is important that it be based on identical information about homes (e.g., beds, baths, square footage, lot size, tax assessment, prior sale price) and that the algorithm itself be consistently applied to all homes in a similar manner. This ensures that there is no preference for some homes relative to others nor are there valuations based on
facts that are not accessible to all Zillow users. Some homes may be very unique in ways that are not well captured by existing data, and the Zestimate may be less accurate on these homes. To provide more data on your Zestimate, you can post your estimated value and comment in the Owners Estimate section indicating your support for a different valuation.

I don't know of any homes that have sold lately around me, how are you calculating my Zestimate?

The number of transactions in a geographic area affects how much we know about prevailing market values of homes in that area.  More transactions provide more data and improve the accuracy of the Zestimate. Also, we use public and user-provided data for house attributes, and some areas report more data than others. The more attributes we know about homes in an area (including yours), the better the Zestimate. Remember that homeowners can also update their home facts if they feel they are incorrect or there are missing values, and the updates may affect the Zestimate value.

Our estimating method differs from that of a comparative market analysis (CMA) done by real estate agents.  Geographically, the data we use is much larger than your neighborhood. Often times, we use all the data in a county for calculation. So though there may be no recent sales in the "neighborhood," even a few sales in the area allow us to extrapolate changes in the local housing market. However, the data we gather does allow the models to incorporate the geospatial (neighborhood) patterns of recent sales.

How accurate is the Zestimate overall?

Our accuracy depends on the home data we receive; see our Data Coverage and Zestimate Accuracy table to see how accurate we are in your area. When it comes to unique homes (e.g., luxury mansions, unusual designs) we are less accurate in our Zestimates.

Can I remove the Zestimate while I'm selling my home (it should be higher)?

It's important to remember that Zestimates track the market, not drive it. People ultimately have more fundamental reasons that drive what they choose to buy or not buy. Our data shows that half of all sales are generally above the Zestimate. To provide more data on your Zestimate, you can post your estimated value and comments  in the Owner Estimate section. The purpose of the Zestimate is to provide data in a user-friendly format to promote transparent real estate markets and allow people to make informed decisions.

Can I use the Zestimate to get a loan?

No, you can't. To get a federally guaranteed loan, a law called FIRREA (the Federal Institutions Reform, Recovery and Enforcement Act) requires an appraisal from a professional appraiser. Without limitation, lending professionals and institutions are prohibited from using the services in making any loan-related decisions. The Zestimate is our estimate of fair market value, a starting point for home buyers and sellers and anyone just plain interested in the value of houses. You can use it in judging market trends, and in calculating all sorts of things for your personal purposes. Click here to view our terms of use.

I have two Zestimates for my home? How do I fix this?

If you see two Zestimates for the same property, you can click on Edit, Report a Problem, then choose incorrect facts from the drop-down menu. However, if you are a homeowner with multiple parcels, and this is the reason there is more than one Zestimate for your address, we match the parcels on record with the county. If you officially combine parcels with the county, they will send us the updated information.
 
 
 
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