To answer this question we need to know two things: 1) the life cycle of your hair and 2) its growth rate.
First, the life cycle of our hair is what controls the amount of time a single hair on our head will grow before it falls out and a new hair grows in its place. For most people that cycle is between two to six years.
Next, you must determine the growth rate of your hair. If your hair is relaxed, the easiest way to determine its growth rate is to measure the “new growth.” This is the section of natural hair that grows from your scalp to the straight relaxed hair between retouches. Typically, relaxers are applied to the new growth every two months. Usually, at those intervals the new growth is about 1” long. This means that on the average, our hair grows about 1” every two months or in other words 6” per year. Some individuals will grow hair a bit faster, others a bit slower.
So how long will it take your hair to grow to your back? Along with many other black women, you may find the hair chart from Thehairfiles.wordpress.com to be a helpful illustration. Let’s assume your hair is shoulder length now and you want to grow it to mid-back length. The distance from the shoulder to mid-back is about 9”. So if we assume that your hair has an average life cycle and growth rate (6” per year), it would take your hair a year and a half to grow the 9” from shoulder length to mid-back length.
Keep in mind, however, that this does not take into consideration any bad experiences you might encounter that could have negative effects on the growth of your hair such as improperly applied relaxers, excessive dryness and brittleness, etc. Remember, for the best result in growing your hair you must keep it healthy.