The year is coming to an end. BAH will change starting January 1, 2013. Depending on where you are, it could go up or it could go down. For example Bremerton, WA went up and Kings Bay, GA went down.
I know that as long as you have BAH it will never go down for you. You will be grandfathered at the higher rate that you had previously. If you were to become an E5 then you would get the current BAH for that rank. Someone else that was an E5 before the BAH went down will keep the higher rate that they were already receiving. I hope I explained this well and I don't confuse anybody. I tried my best.
Click HERE for the link to the BAH Calculator. All you need is the zip code of your current duty station and the pay grade.