ANDY'S ANSWER: If you can remember when you first noticed your breasts starting to bud, you can expect your period to occur between 2 and 2 1/2 years after that.
There are other signs as you get closer to your period. One will be a growth spurt. Also your breasts will have started to actually grow. You will start getting underarm hair, and you might notice a thick whitish-coloured mucas discharge in your underwear. All of these signs indicate that your period is probably only months away.