Jason Gonsalves worked hard to turn his 6,500-square-foot stucco-and-stone home in the suburbs of Sacramento into the ultimate grown-up party pad, complete with game room, custom wine cellar and an infinity-edge pool overlooking Folsom Lake. When interest rates fell recently, Mr. Gonsalves, who runs a lobbying firm, looked into refinancing his $750,000 mortgage. That’s when he got startling news—the home had dropped more than $200,000 in value while he was renovating.
Or at least, that’s what one real-estate website told him. Another valued the house at only $640,500. And these online estimates left him all the more confused when a real-life appraiser, assessing the house for the refinancing loan, pinned its value at $1.5 million. “I have no idea how those numbers could be so different,” Mr. Gonsalves says.
Right or wrong, they’re the numbers millions of consumers are clamoring for. Web-driven companies like Zillow, Homes.com and Realtor.com are reshuffling the deck, giving home shoppers and owners estimates of what almost any home is worth. People have flocked to the data in startling numbers: Together, four of the biggest sites that offer home-value estimates get 100 million visits a month, with web surfers using them to determine what to ask or bid for a home, or whether to refinance.
But for figures that can carry such weight, critics say, the estimates can be far rougher than most people realize. Valuations that are 20% or even 50% higher or lower than a property’s eventual sale price are not uncommon, as the sites themselves acknowledge. The estimates frequently change, too—sometimes by hundreds of thousands of dollars—as sites plug new data into their algorithms.
All of the competitors make it clear their numbers are guesstimates, not gospel. “A Trulia estimate is just that—an estimate,” says a disclaimer on that site’s new home-value tool. Zillow goes a step further, publishing precise numbers about how imprecise its estimates can be. And every major site urges home-price hunters to consult appraisers or real-estate agents to refine their results.
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