No, Zillow uses a generalized algorithm that crunches data from public property records, tax records. Recent home sales in the area and user submitted information to come up with an approximate market value for home emphasis on user submitted information. Just like Wikipedia, it's just people adding and subtracting improvements for what they think their home is worth or want it to be worth. There's actually a 40% margin of error with its estimate versus having a realtor price at your home where they use a comparative market analysis. Comparative market analysis or CMA is an estimate of the value of a specific property by evaluating similar ones that have recently sold in the area, usually within a given length of time or distance away from the subject property.