Snap shareholders can stop freaking out. IPO's poor start is not unusual

Investors have been disappointed by the weak stock performance in the first few days after the Snap IPO. It appears that the social media company may not be the new Facebook after all.

But wait — Snap's poor showing makes it more like Facebook than not. After all, Facebook, today's high-flying tech stock, also plummeted in its first week on the market in May 2012. Shares didn't recover to the first-day opening price until over a year later in September 2013.

In fact, about 40 percent of all IPOs in the past decade were down five days after their first trading day, according to a CNBC analysis of FactSet data. Bigger IPOs bringing in at least $2 billion did poorly even more frequently — down about 65 percent of the time in the same time frame.

Snap's 11 percent drop from its initial opening price as of Tuesday evening puts it among the worst 10 percent of IPOs for the first five days (the median is a 0.12 percent drop). So the company's first few days are notably bad.

But knowing that Snapchat is performing poorly now doesn't tell us much at all about its long-term prospects.

For the nearly 2,000 IPOs over the last decade, there isn't a relationship between the first week and the first year's returns. That means that a stock that tanks right off the bat is just as likely to be a winner in 52 weeks as one that's popular on day one.

For the biggest IPOs like Snap, companies that drop at the beginning are more likely to be down still a year later. Perhaps the added attention from investors and the media turns a bad start into a self-fulfilling prophesy.

But that pattern disappears the longer the stock is around, according to our data. Like Facebook, some early flops will turn into powerhouses, while other early success stories will fall apart.

This is not to say that Snap will end up being a great buy — there are plenty of other concerns about the company, like its slowing user growth and spending on hosting. Many IPOs are simply duds.

Just look at the table above: 70 percent of the big IPOs in the last decade are worse investments than the S&P 500 if investors bought at the beginning of the first day.

The average IPO since 1980 has underperformed the market, even if buyers got the offer price and not the first day's open, according to data compiled by professor Jay Ritter of the University of Florida.

Based on previous offerings, investors should expect Snap to be down for at least the next year, and then the new stock will sink or swim independently of its its early floundering.

Disclosure: CNBC parent NBCUniversal is an investor in Snap.