Good Faith Media: Global Christian Population to reach 3.3 BN by 2050.

[Astreja]

There's one factor in this alleged Christian population growth scenario that needs to be kept in mind: Religious organizations aren't very good at removing people from their membership lists when those individuals decide that they want nothing to do with the church. Even if there were 3.3 billion people listed as "Christian" by 2050, a lot of those people will be baptized-at-birth nonbelievers or different-believers, and a lot more will be indifferent, infrequent churchgoers. "They were never True Christians™" - except when the numbers need to be inflated.

This is all a moot point, of course. Even if everyone on Earth believed the same thing, that wouldn't make it true.