For the last five years, instant messaging app Slack has found success as the app that employees at startups and big companies alike use to talk to each other.

That success has led the company itself to growth: TechCrunch reported Wednesday that the company is looking to raise $400 million in an upcoming round, which would bring the company’s value to $7 billion – that is, $2 billion more than the valuation it achieved when it last raised funding in late 2017.

As this chart from Statista shows, Slack’s user base has been growing exponentially since 2015, with the most impressive uptick coming in the last year. Also of note is that while Slack offers a free version, about 25% of its total userbase pays up for the premium tiers.

However, it faces stiff competition: Microsoft Teams, included in the Office 365 suite, is rapidly nipping at Slack’s heels.