That depends on what length you want to keep your hair during the grow-out. If you shave (buzz) all your dyed hair off, it would take you just minutes to achieve naturally gray hair. If you cut your hair into a pixie cut, the average length of time to grow out your gray roots is 3-6 months. If you want to keep your hair shoulder-length or longer, it can take about 2-3 years depending on the rate of hair growth. My hair grows faster than average (average is 1/2" per month; my hair grows 3/4" a month) and it took me 2 1/2 years to grow out my roots to shoulder-length. You can check out my cold turkey transition story to see progress photos. (I need to update that post, however, as still had a wee bit of dye left on the ends at that point.)