What chapter does Attack on Titan season 2 finish at? I just finished the season 2 of Attack on Titan and I want to start to read the manga.

Which chapter should I start from?
Yes, the events in Episode 37 of Attack on Titan (Season 2, Episode 12) corresponds to Chapter 50 in the manga. That means that if you wanted to pick up right after Episode 12, as everyone mentioned above, it would be Chapter 51 (Volume 13) of the manga. Just for anyone looking for an episode-manga equivalent of Season 1 and Season 2 of Attack on Titan: 

Season 1: 



Season 2



This is the best equivalency I've come up with. Please note that some things were covered in the manga and not the anime, and there were some events that occurred in difference places than in the anime.