If there’s something that seems to be paying off for casual developers, it’s taking a popular game and making it free-to-play. Last month, it turned out that Temple Run had quadrupled its income when it went free, and now it seems like Jetpack Joyride is repeating this particular piece of history.

According to developer Halfbrick, Jetpack Joyride has seen a total of 14 million downloads. That’s certainly impressive, but what’s especially interesting is that 13 million downloads took place after the game became a free-to-play title in mid-December.

It also turns out that the game has generated a lot more money since it was discounted to the low, low price of zilch. Halbrick’s chief marketing officer Phil Larsen explained to Joystiq that roughly five to ten percent of users are spending at least a dollar on in-app purchases (which is how much the game was selling for in December).

Fans of the game will also be excited to learn that Halfbrick is gearing up to release a free update for the game next month. Oh, and it’s going to be massive. According to Larson, “It’s the biggest one we’ve done so far.”

[via ShackNews]