Zestimate home valuation is a tool offered by Zillow that provides an estimate of the market value of a home. It makes calculations for about 100 million homes nationwide, as of 2015. The value does not replace an official appraisal but instead offers a starting point for sellers and buyers.
Zillow updates Zestimate three times per week based on data points submitted by users and the public. The accuracy of the estimate depends on the availability of data on a particular area. Zillow states that Zestimate has a median error rate of 8.3 percent nationally. Homeowners can edit the included facts about their homes to improve the accuracy of the tool.