Hi R.:
I actually got lots of great advice about this same topic here in the last few months. I was considering stopping the bottle at 12mo., but my doc said that we shouldn't stop the formula until she drinks milk instead (in a sippy cup), so she still gets the nutrition she needs. Well, my daugther has always been a great eater, but she HATED milk!
So, at 12 mo., we reduced our bottles to two a day (one morning/one night/and sometimes one in the middle of the night) and then waited until she started to like milk, which didn't happen until around 16mo. Then, we cut back to one formula bottle before bed, for a few weeks, before we cut it out altogether! It was only a day or two of whining and then she didn't seem to notice it was gone. And it's amazing the money you save on formula. wow. But, I agree with the other ladies - you need to wait until the time is right for your baby and don't try to force it! Be sure she's good with using her sippy and will drink milk out of it. Good luck!