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LJ HairLab

the hair growth edit

Hair Growth and Length Retention Guide

Growth rates, retention and length goals you can plan.

Free hair growth tools

Calculator

Hair Growth Calculator

See when you will reach shoulder, bra-strap or waist length based on growth rate, retention and trims.

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Chart

Interactive Hair Length Chart

Enter your height and see where every length level — from chin to tailbone — falls on your body.

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Calculator

Trim Schedule Calculator

Find your ideal trim interval and see how trims affect yearly length gain.

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Tracker

Length Retention Challenge Tracker

Track monthly length in five zones and finish a 90-day retention challenge.

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Tracker

Hair Progress Photo Comparison

Line up before and after photos side by side or with a slider — privately, in your browser.

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Calculator

Hair Length Converter (cm ↔ inches)

Convert hair length between centimeters and inches and see which length level it is.

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Calculator

Hair Growth Rate Calculator

Enter two length checks and the dates to see your real growth and retention rate per month.

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Calculator

Terminal Length Calculator

Estimate the longest your hair can grow from your growth rate and growth-phase length.

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Calculator

Haircut Grow-Out Calculator

See how long it takes to grow out bangs, a pixie, a bob or a big chop to the length you want.

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Checker

Split Ends Checker

Identify the kind of split ends you have, what causes them and how much to trim.

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Tracker

Scalp Massage Timer

A guided four-minute scalp massage that walks you through each zone with a timer.

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Planner

Postpartum Hair Shedding Timeline

Enter your baby’s birth date to see when shedding usually starts, peaks and settles — and when to see a doctor.

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Calculator

Hair Donation Length Calculator

Check whether your hair is long enough to donate and how long it will be afterwards.

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Most people who feel their hair “won’t grow” are actually losing length about as fast as they gain it. This guide explains how hair growth works, what realistic numbers look like for textured hair, and where length really goes — so you can spend your effort on what moves the needle.

How hair grows

Each hair grows from a follicle in a repeating cycle. In the growth phase, which lasts several years, the follicle keeps producing hair. A short transition phase follows, then a resting phase, after which the hair sheds and a new one starts growing in its place. Because every follicle runs on its own schedule, you lose some hairs every day. The American Academy of Dermatology describes shedding about 50 to 100 hairs a day as normal.

How long your growth phase lasts sets your personal maximum length. Two people who grow hair at the same speed can still end up with different maximum lengths because their follicles grow for different numbers of years.

How fast does textured hair grow?

Half an inch a month is the figure you’ll see everywhere. Research that measures growth directly has found wide variation between individuals and between groups; one study of African hair recorded an average of about 256 micrometers a day, which works out to roughly 0.3 inches a month. Your rate may be faster or slower — the only way to know is to measure it.

Pick one section, stretch it, and measure from scalp to ends on the same day each month for two or three months. If you relax your hair, measure the new growth just before a touch-up and divide by the number of months since your last one.

Growth vs. retention

Growth happens at the scalp; length is what’s left at the ends. Tightly coiled hair bends and twists along the strand, which makes it more likely to knot and break during combing and styling. Every time ends snap off, you lose some of the growth you made at the roots.

That’s why length retention matters so much. If your hair grows half an inch a month but you lose a quarter inch to breakage, your net gain is half what you expected. The hair growth calculator lets you change your retention and trim schedule to see how much sooner you’d reach your goal by keeping more of what grows.

What actually helps you keep length

  • Detangle gently and with plenty of slip. Use conditioner, work in sections and start at the ends.
  • Protect your ends. Styles that tuck the ends away help — as long as they aren’t pulling on your scalp.
  • Limit high heat and chemical overlap. Both weaken the strand.
  • Keep hair moisturized. Dry, brittle hair breaks more easily.
  • Cover your hair at night with satin or silk to reduce friction.
  • Look for single-strand knots and snip them carefully rather than ripping through them.

Do trims help hair grow?

Trimming doesn’t change how fast your hair grows, because growth happens in the follicle, not at the tips. What trims can do is remove split ends before they travel further up the strand and cause more breakage. The goal is to trim only as much and as often as your ends actually need — the growth calculator shows how a trim schedule changes your yearly gain.

Does diet matter?

Hair follicles need nutrients like any other tissue, and research reviews have linked certain deficiencies, such as low iron, with increased shedding. But supplements haven’t been shown to speed growth in people who aren’t deficient, and high-dose biotin can interfere with some laboratory tests. If you’re worried about your diet or notice extra shedding, ask your doctor about testing before you start taking anything.

Know your length levels

Length goals are usually described by where hair falls on the body: shoulder length (SL), armpit length (APL), bra-strap length (BSL), waist length (WL) and so on. Because torsos differ, the same number of inches lands in a different place on different people. The interactive hair length chart scales each level to your height so your goal is realistic for your body.

When to see a dermatologist

See a board-certified dermatologist if you notice bald patches, a widening part, thinning at the edges or temples, sudden heavy shedding, or scalp pain, itching or scaling. These can have medical causes that need a proper diagnosis, and earlier care usually means more options.

Frequently asked questions

How long does it take to grow 6 inches of hair?

At a steady half inch a month with no breakage or trims, about a year. In practice, breakage and trims slow most people down, so 15 to 24 months is common. The hair growth calculator gives you a date based on your own numbers.

Why does my hair seem stuck at the same length?

Usually because the ends are breaking about as fast as the roots grow. Measure your growth at the roots and look closely at your ends — short broken pieces after detangling are a sign of breakage.

Does trimming make hair grow faster?

No. Hair grows from the follicle at the scalp, so cutting the ends doesn't change the growth rate. Trims can help you keep length by removing split ends before they cause more breakage.

Can vitamins make my hair grow faster?

Not if you aren't deficient. Research hasn't shown that supplements speed growth in people with normal nutrient levels, and high-dose biotin can interfere with some lab tests. Ask your doctor about testing first.

Sources

Last reviewed:

  1. Paus R, Cotsarelis G. The biology of hair follicles. N Engl J Med. 1999;341(7):491-497. Hair grows in cycles (anagen, catagen, telogen); growth happens in the follicle and the length of anagen limits maximum length.
  2. Loussouarn G. African hair growth parameters. Br J Dermatol. 2001;145(2):294-297. Afro-textured hair grew about 256 µm/day in the study sample — slower than Asian and Caucasian samples.
  3. Loussouarn G, Lozano I, Panhard S, et al. Diversity in human hair growth, diameter, colour and shape. An in vivo study on young adults from 24 different ethnic groups observed in the five continents. Eur J Dermatol. 2016;26(2):144-154. Growth rate, diameter and curl shape vary widely between and within groups.
  4. Khumalo NP, Doe PT, Dawber RP, Ferguson DJ. What is normal black African hair? A light and scanning electron-microscopic study. J Am Acad Dermatol. 2000;43(5 Pt 1):814-820. Tightly coiled hair forms knots and breaks more easily during grooming.
  5. Bryant H, Porter C, Yang G. Curly hair: measured differences and contributions to breakage. Int J Dermatol. 2012;51 Suppl 1:8-11. Curlier hair breaks more during combing; breakage is a key limit on length.
  6. American Academy of Dermatology. Do you have hair loss or hair shedding? Shedding 50–100 hairs a day is normal.
  7. Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The role of vitamins and minerals in hair loss: a review. Dermatol Ther (Heidelb). 2019;9(1):51-70. Review of evidence linking micronutrient deficiencies to hair loss and the limited evidence for supplementation without deficiency.
  8. Soleymani T, Lo Sicco K, Shapiro J. The infatuation with biotin supplementation: is there truth behind its rising popularity? A comparative analysis of clinical efficacy versus social popularity. J Drugs Dermatol. 2017;16(5):496-500. Little evidence that biotin helps hair in people without deficiency.

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