The tool then provides a private estimate to the homeowner. The private "Price This Home" valuation remains separate from the public Zestimate. (Separately, the company this year started offering homeowners the ability to correct facts about their home and see that new information reflected immediately in the Zestimate for their home .) Redfin says its new estimator tool uses an unprecedented amount of data, including comparable home sales and listings, to predict the value of a home within a 2 percent margin of error on homes listed for sale, and 6 percent for homes that are not for sale. Because the company is an online brokerage, Redfin says it has has full access to large amounts of home data from multiple listing services, in contrast with services such as Zillow that aren't brokerages. Zillow's median error across the country is 7.9 percent for the Zestimate. The company says it's too early to derive a margin of error for the new Price This Home feature.