Snapchat is still rallying — here's how long it takes on average for a hot IPO to crash (SNAP)

In its first two trading sessions, the Snapchat parent has gained as much as 69% above the $17 price of its initial public offering.

Analysts and investors are continuing to question whether the company is overvalued and how much ad-revenue share it will be able to steal from digital giants like Facebook and Google.

The enthusiasm around Snap could last at least a few more weeks if the history of major IPOs repeats itself.

"Our composite path of the largest 20 IPOs shown below projects a peak 38 trading days (two months) after the first trade date on average followed by a substantial four-month decline," said Tom Leveroni and Shourui Tian of Nautilus Investment Research in a note. Their composite includes Goldman Sachs' 1999 debut and Alibaba's offering in 2014.

They added that the issuing companies and investment banks had been quite good at selling near the market tops.

"It's well accepted that investors are overpaying for Snap based on expected sales and earnings, but it doesn't seem to matter," Jasper Lawler, a senior market analyst at London Capital Group, said in a note. "With such exuberance in the marketplace, Snap's timing is impeccable."

Snap's surge in the past two days has created flashbacks of other large tech IPOs. Twitter opened at $45.10, 73% above its initial offering price in November 2013. It peaked two months later before dropping below its IPO price. Investors who bought at the debut and haven't sold are down 62% amid slow user adoption and executive departures from Twitter.

Conversely, Facebook fell below its offering price the day after it went public in May 2012. But it's up 257% from its debut.

Interest in Snap's shares could remain high amid media coverage and more investor demand, said Ihor Dusaniwsky, the head of research at S3 Partners. But short interest — a gauge of whether investors think the stock price will fall — is likely to increase, too.

"We expect that 10% to 20% of the initial offering will be shorted in the first week of trading, which roughly translates into $500 million to $1 billion of short interest right from the start," Dusaniwsky said.

Snapchat is still rallying — here's how long it takes on average for a hot IPO to crash (SNAP)

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