Terminal Length Calculator

How terminal length hair estimates are worked out

Every hair on your head grows for a few years, rests, sheds and is replaced. The growing part of that cycle is called anagen, and its length sets a ceiling on how long one strand can ever get. That ceiling is what people mean by terminal length. The arithmetic is simple:

terminal length  = growth per month × 12 × years a strand keeps growing
expected length  = terminal length × share of growth you keep
years to reach   = (expected length − current length) ÷ (growth per year × share kept)

The two numbers behind it

Growth rate is the one you can measure. Half an inch (1.27 cm) a month is the common rule of thumb; a study of Afro-textured hair measured a sample average closer to 0.31 inches a month, and individual rates vary a lot. If you want your own figure, take two length checks a few months apart with the hair growth rate calculator.

The growth phase is the one you cannot measure. It is usually described as lasting about 2 to 7 years, it is largely inherited, and it differs between follicles on the same head. At half an inch a month that range alone gives anything from 12 to 42 inches. So move the slider and read the result as a range of what-ifs.

Why retention matters more

The formula assumes a strand survives for its whole growth phase. In real life the oldest part of the hair — the ends — has been washed, combed and styled thousands of times, and it wears away. If the ends break at the same pace as the roots grow, length stands still years before any strand reaches its terminal length. The retention slider shows this: at 100% you see the theoretical ceiling, and every step down is length lost to breakage. For most people that gap, not genetics, is what stops their length.

Where it falls on the body

Lengths are matched to the usual length levels — ear, chin, shoulder, armpit, bra strap, mid-back, waist, hip, tailbone and classic — measured from the crown down the back on stretched hair, for a height of 5 ft 4 in. The hair length chart scales those levels to your own height.

What this calculator cannot tell you

It cannot tell you your real growth phase, and it cannot tell you that you have reached terminal length. Hair that has been the same length for a year or two is much more often breaking than finished growing. Curly and coily hair also shrinks, so measure stretched. And if your hair is shedding heavily or thinning in patches, that is a different question from length: see a board-certified dermatologist.