In Halo: Reach for the Xbox 360, your rank is based on the credits you receive over the course of the game. Unlike previous games, you don’t just gain rank by playing online, since you can get credits from all game types.
Here is a full list of the lifetime credits you need to get each rank:
Recruit – 0 Credits
Private – 7500 Credits
Corporal – 10000 Credits
Corporal Grade 1 – 15000 Credits
Sergeant – 20000 Credits
Sergeant Grade 1 – 26250 Credits
Sergeant Grade 2 – 32500 Credits
Warrant Officer – 45000 Credits
Warrant Officer Grade 1 – 78000 Credits
Warrant Officer Grade 2 – 111000 Credits
Warrant Officer Grade 3 – 144000 Credits
Captain – 210000 Credits
Captain Grade 1 – 233000 Credits
Captain Grade 2 – 256000 Credits
Captain Grade 3 – 279000 Credits
Major – 325000 Credits
Major Grade 1 – 350000 Credits
Major Grade 2 – 375000 Credits
Major Grade 3 – 400000 Credits
Lt. Colonel – 450000 Credits
Lt. Colonel Grade 1 – 480000 Credits
Lt. Colonel Grade 2 – 510000 Credits
Lt. Colonel Grade 3 – 540000 Credits
