Google expected to post big revenue, but watch out for margins

Google headquarters in Mountain View, Calif.
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While Google is widely expected to post an impressive quarter when it reports earnings after the bell on Wednesday, investors will want to keep a close eye on the company's operating margins.

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Analysts surveyed by Thomson Reuters estimate the company will report earnings of $6.41 per share on revenue of $15.54 billion, which is a 11 percent and 11 percent increase year-over-year, respectively.

The company has also seen organic revenue growth of 20 percent for the past 16 quarters, according to a recent note by RBC Capital Markets.

But just because it's Google doesn't mean the growth will last forever.

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"The investor community has largely been focused on the top-line and bottom-line numbers, and they look pretty good," said Brian Wieser, an analyst at Pivotal Research. "But the stuff in the middle is telling a different story."

Wieser, who has a "hold" rating on the stock with a $580 price target, said that there is margin erosion in Google's core business. The company is keeping more of every dollar it earns and eventually that will likely backlash on the stock, he said.

"As the network cull comes to an end, the trend begins to reverse," Wieser said. "It's got to end sometime, it's hard to say which quarter it will be. But at some point it will matter."

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Google has also made big pushes into new product categories with its investment in things like wearables, cars and drones. Its move into these areas will eventually increase pressure on margins.

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"Operating margins should continue to fall due to the company's expansion into activities beyond self-service paid search," Wieser said in a recent note to clients.

"While absolute profits and cash will continue to grow, the disconnect around the degree to which Google will grow absolute vs. percentage margins is probably not fully incorporated in the market at this time."

Google's non-GAAP operating margins in the last quarter stayed relatively flat, but will likely decline to 41.8 percent in the first quarter versus 43 percent margin last quarter because of the company's seasonal operating expenses, said Mark Mahaney, an analyst at RBC Capital Markets, in a recent note to clients.

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Besides margins, investors will be watching Google's paid click and cost per click (CPC) business and the company's search ad business that offers richer ads known as Product Listing Ads.

These ads allow advertisers to display an image, product and price data as well as merchant information.

"With rich product information (image, size, color options, etc.) embedded directly in the search results, Product Listing Ads (PLAs) make Google appear more like Amazon," said Brian Pitz, an analyst at Jefferies, in a note to clients Tuesday.

"We believe these ads will generate faster revenue growth, and thus we have been tracking their rollout over time. In the near term, we believe PLAs are a key catalyst as Google Shopping recently transitioned to a paid service."

According to Pitz's note, the firm is also anticipating 28 percent year-over-year growth for paid clicks and a 10 percent year-over-year decrease in CPC.

"Overall we think paid clicks remains the best indicator of a healthy ad ecosystem," Pitz said in his note. "CPC declines are not a concern as long as they are offset by paid click growth."

—By CNBC's Cadie Thompson