Zillow shares dropped as much as 12 percent Tuesday morning, after the company held a conference call that included guidance significantly below Wall Street estimates.

The stock had traded up more than 3 percent prior to a premarket halt just before 9 a.m. ET. When Zillow resumed trading about an hour later, the weak guidance took a toll on share prices: The stock opened about 12 percent down, before paring much of that loss.

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On the call, Zillow CEO Spencer Rascoff announced that the company is expecting EBITDA in the range of $80 million to $85 million for the full year 2015—Wall Street had expected that figure to be about $146.8 million, according to FactSet.

"The work we are doing this year lays the foundation for an incredibly bright 2016 and 2017. However, 2015 is a transition year and we're trending a couple quarters behind where we'd like to be, due to the protracted [Federal Trade Commission] approval process which only ended two months ago," Rascoff said, referring to the recent deal to merge with Trulia.

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Rascoff also said the company expects pro forma revenue at about $690 million for the year. Analysts had expected the company to post revenues of about $752.97 million in 2015, according to Thompson Reuters. In a message to CNBC, Rascoff described 2015 as "a little messy," but admitted that the Trulia business is "softer than we'd like" in part because of the FTC process. On the call, Rascoff also explained the below-estimate guidance as a consequence of "some decisions to establish our foundation for growth that will impact our results in the near term." He cited a decrease in advertising placements for the Trulia platform, among other moves.