It depends on how long you want your hair to be. 2 years= 24 months, hair grows about .5in/month, so that estimate is considering you want to maintain hair that is about 12 in long. Of course if you want to keep your hair in a shorter style (say 6 in) it will take less time (about a year), but you should also keep in mind that it might not look or feel as though your hair is growing (unless it is stretched or straightened) because the new growth will have shrinkage that the permed part doesn't have (so if you were to trim 2 permed inches after 4 months, technically you should have just as much length because you will have about 2in of growth, but it will probably appear shorter).