When you're trying to grow out a short cut, hair growth seems to take forever. Your hair doesn't grow continuously as your fingernails do. The hair on the scalp goes through three phases of growth. The vast majority of hair on your head is in the anagen, or growing, phase.
During the anagen phase, your primary hair cells divide every 24 hours. Hair in this phase of development grows about 0.35 millimeters daily. Over the course of a 30-day month, this yields approximately a 0.4-inch growth. This phase of growth lasts for two to six years.
Catogen and Telogen Phases
The catogen phase lasts just a day or two and marks the point at which hair growth stops. Just 1 percent or fewer of the hairs on your head are in this phase at any given time. The catogen phase is followed by the telogen phase, the point at which the shape of the hair at the follicle changes to a club shape and the hair prepares to fall out naturally during brushing. This telogen phase lasts three to four months. About 15 percent of your hairs are in this phase at any given time.