How is belt rank calculated? If I wait one game before ranking up, will I become rank 1?

Belt rank? Bro I'm confused. Do you mean the global rank? If that's what you mean then you should try to google the "Elo rating system". Hope this helps.

No I mean belt rank, the rank it displays when you type "/stats".

He might be asking for the rank displayed in the Usercard, which isn't the same as the ingame rank. (The one displayed in /stats)

If it is the rank within your belt players, the closer you are to the next belt the higher should your rank be. If this rank is only related to forum (posts, activity,...), you will need more posts in order to reach rank 1. If, however, it is only related to ingame, you will have to win more games to get a better rank.

Thank you.

The forums are an older ranking system that isn't used anymore. The new in-game ranking system (the current one) is based off the "Elo system".

http://en.m.wikipedia.org/wiki/Elo_rating_system