The usual calculation is per 42 days, or per "verison". A F2P account can get about 80, and monthly card account can get about 110.
It varies every version.
Feel free to use this sheet as well; it's very helpful.
https://docs.google.com/spreadsheets/d/1X9fyml5ldU4fWd4ry1ckIp84J6arImz1m5KqHzmbhr8/edit#gid=48245395