Zillow uses data both from the public domain and submitted by users to compute its Zestimate value ranges, and it uses a formula that takes into account a home's physical features, past sale prices and tax records, along with other items. The company notes that the values are estimates and not official home values that a professional appraiser or real estate agent can provide. Calculations are done three times a week to provide frequent updates.
Incorrect information about a home's price history, tax history or updates can cause the Zestimate to be too low or high for a home. Homeowners can submit an update on the Zillow website, although the Zestimate may not change right away or at all, according to the Zillow website.