Shoulder length:In general, assuming that you are starting from a fresh, bald shave it should take you about 2 to 2 ½ years to reach shoulder length with great hair care.
Armpit Length: Between shoulder length and brastrap length lies another popular hair length in the hair forum world known as “armpit length” (APL). This is the length along the back that is defined by the imaginary line drawn across the back where the arm meets the back (armpit) and then travels across to the other side. From shoulder length, APL could be anywhere from 6-15 months away- obviously depending on individual trim rates and retention.
Brastrap Length: About 9 months to 18 months from there, you can expect to be reaching brastrap length (BSL). I’ve seen it done in both. This is the length along the back where the bottom strap of your bra rests.* This length is typically 3 years out from a clean shave.
Midback/Waist: From a clean shave, it will take you about 3-4+ years of healthy hair care to reach midback length (between brastrap and waistlength), and possibly another six months to a year to reach waist length considering the length of your torso/back and any trims you may do along the way.
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