Fitbit IPO goes from walking to running

Fitbit going strong

The Fitbit IPO—and the wearable market—just got a lot hotter. Fitbit is scheduled to price Wednesday and begin trading at the NYSE on Thursday.

Overnight, the company dramatically upped the offering size, from 29.9 million shares at $14 to $16 per share, to 34.5 million shares at $17 to $19.

That's big. At the midpoint, the offering size has gone from $448 million to $621 million, a jump of 39 percent.

The market cap of the company is now roughly $4.5 billion.

Why the big jump in the size and price? Two reasons:

1) Demand

By the end of the third quarter, it had sold more than 20.8 million devices. It holds the leading position in the U.S. fitness activity tracker market, with an 85 percent share of that market in dollars, according to Renaissance Capital, the IPO ETF (IPO) manager.

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2) Big revenue growth, with profits

Four years ago, in 2011, it had $15 million in revenue. In the latest trailing 12 months, revenue has grown to $973.4 million. And it is profitable, with $170.9 million in net income.

That's pretty amazing. Another wearable company, GoPro (GPRO), is only growing roughly by 35 percent.

Another anomaly: It hasn't taken tons of early venture funding. Two venture capital groups, Foundry Group and True Ventures, own roughly 50 percent of the company, but the outside capital was only $70 million. The founders, James Park and Eric Friedman, each own more than 10 percent.

Of course, there are competitors. Jawbone and Garmin (GRMN) are the other major rivals, and obviously Apple (AAPL) and the Apple Watch is the coming big competitor. Xiaomi, the Chinese company, also has rival products coming at a lower price point.