“It’s a good thing that there’s always room for one more, because the tavern has now welcomed over 70 million players!” Blizzard said. “On top of that, with Journey to Un’Goro, Hearthstone had more players playing together on the same day—around the whole world—than at any point in its history!”
To give you some idea of the growth of Hearthstone, the digital card game was at 30 million players in May 2015 and 50 million players by April 2016. So 20 million a year? That’s not a bad trajectory at all.
Source: Hearthstone