Population Milestones

Your population is the number of people living in your nation, and it increases everyday. Upon reaching certain milestones you will unlock special settings for your nation (see list at bottom).

It will start at 5 million, and increase exponentially as follows:
5 million to 10 million - 1 million per day
10 million to 20 million - 2 million per day
20 million to 32 million - 3 million per day
32 million to 40 million - 4 million per day
40 million to 50 million - 5 million per day
50 million to 62 million - 6 million per day

By my calculations you should reach 62 million in 20 days, after 62 million, population increases 5-7 million per day randomly.
Below are the lower and upper extremes of how many days to the population milestones:

58 days maximum to 250 million.
108 days maximum to 500 million.
158 days maximum to 750 million.
208 days maximum to 1 billion.

47 days minimum to 250 million.
83 days minimum to 500 million.
119 days minimum to 750 million.
155 days minimum to 1 billion.

47 - 58 days to 250 million.
83 - 108 days to 500 million.
119 - 158 days to 750 million.
155 - 208 days to 1 billion.

250 million: Your nation will receive an issue that allows you to set a Capital City in some circumstances.

500 million: You can write a custom pretitle in your Settings.

750 million: The Leader issue.

1 billion: The Faith issue.