According to the CDC, scalp hair grows an average of one-half inch per month. If your hair is two inches long and you’re aiming for shoulder length (about 12 inches) growth, that adds up to a little less than two years to reach your goal.
But your hair growth cycle is as unique as you are, so there’s really no one-size-fits-all answer. At any given time, your hair is dispersed into different phases of the growth cycle, taking turns adding inches to your length in the growth phase, pausing in the resting phase, and making room for new growth by entering the shedding phase.