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LJ HairLab

free calculator

Hair Growth Calculator

Find out when you'll reach your length goal. Enter your current length and pick a goal — we factor in breakage, trims and shrinkage.

Your hair

in

Crown to ends, measured at the back.

Measured
Goal

Length levels scale with your torso.

Growth, retention and trims
in

Default 0.5 in (1.27 cm). Studies of Afro-textured hair measured slower averages — measure your own over 2–3 months for the best estimate.

80%

How much of your growth you keep after breakage and split ends. 100% = no breakage.

in
wk

0 = no trims

How to use the Hair Growth Calculator

  1. Enter your current length

    Measure from the crown to the ends at the back of your head. If you measured curls as they dry, choose “Shrunken” and set your shrinkage so the calculator works in stretched length.

  2. Pick your goal and height

    Choose a length level such as APL, BSL or waist length, or switch to an exact length. Your height scales where each level falls.

  3. Fine-tune growth, retention and trims

    Open “Growth, retention and trims”. Keep the default 0.5 in a month or enter your own measured rate, set how much length you keep after breakage, and add your trim routine.

  4. Press Calculate

    You get the time to your goal, the month you should get there, your net monthly gain and what breakage and trims cost you — plus how much sooner 90% retention would get you there.

  5. Save your plan

    Download the PDF tracker to log a measurement every month, or copy the link — it reopens this exact result.

How to use the Hair Growth Calculator (68 s)

How it works

The calculator works out how much length you keep each month, then divides the distance to your goal by that number. Everything is done in stretched inches, because that is how length levels are judged. 

net gain per month = growth rate × retention − trim × (4.345 ÷ weeks between trims)
months to goal     = (goal length − current length) ÷ net gain

1. Growth rate

Half an inch (1.25 cm) a month is the default because it is the figure most people use. Research on Afro-textured hair has measured slower averages — one study found about 256 µm a day, roughly 0.3 in a month — and rates differ a lot from person to person. If you have tracked your own growth, use that number instead.

2. Length retention

Hair that breaks at the ends never shows up as length. Coily strands bend and twist along their length, which makes them more likely to knot and snap during combing. The retention slider is the share of growth you keep after that breakage. Moving it from 70% to 90% often shortens the timeline more than any growth product could — the dashed line on the chart shows that scenario.

3. Trims

A trim of ¼ in every 12 weeks removes about 0.09 in a month (there are 4.345 weeks in an average month). The calculator subtracts that from your monthly gain. If trims remove as much as you retain, it tells you how far apart they need to be for you to make progress.

4. Shrinkage and height

If you measured curls as they are, choose “Shrunken” and set your shrinkage; 6 in shrunken at 50% shrinkage is 12 in stretched. Length levels are drawn for a 5′4″ woman and scaled to your height, since a longer torso puts bra-strap length lower.

Limits

  • Growth is not perfectly steady — it can vary with season, health and age.
  • Each hair grows only for a few years before it rests and sheds, so everyone has a personal maximum length.
  • This is a planning tool. It cannot predict medical hair loss — if you see bald patches or sudden shedding, see a dermatologist.

How long to each length level from shoulder length

Level Length (5′4″) Keep 0.25″/mo Keep 0.35″/mo Keep 0.45″/mo
Armpit length (APL) 15″ / 38 cm 1 year9 months7 months
Bra-strap length (BSL) 18″ / 46 cm 2 years1 year 5 months1 year 1 month
Mid-back length (MBL) 21″ / 53 cm 3 years2 years 2 months1 year 8 months
Waist length (WL) 25″ / 64 cm 4 years 4 months3 years 1 month2 years 5 months
Hip length (HL) 30″ / 76 cm 6 years4 years 3 months3 years 4 months
Tailbone length (TBL) 34″ / 86 cm 7 years 4 months5 years 3 months4 years 1 month
Classic length (CLASSIC) 38″ / 97 cm 8 years 8 months6 years 2 months4 years 10 months

Starting from shoulder length (12″). “Keep” is net gain after breakage and trims. Lengths measured from the crown, stretched.

Frequently asked questions

How long does it take to grow hair from shoulder length to bra-strap length?
About 6 inches separate shoulder length and bra-strap length on an average 5′4″ frame. If you keep 0.35 in a month after breakage and trims, that is roughly 17 months. With almost no breakage and no trims at 0.5 in a month it would be about a year. Enter your own numbers above for a date.

How fast does Black hair grow?
The figure most people quote is half an inch (1.25 cm) a month, but a study of African hair measured an average of about 256 µm a day — closer to 0.3 in a month — and individual rates vary a lot. The best number is your own: measure the same section for two to three months.

My hair grows, so why is it not getting longer?
Because length is growth minus loss. Tightly coiled hair knots and breaks more easily, and ends that snap off cancel out growth at the roots. The retention slider shows how much faster you reach a goal when you keep more of what grows — for many people that matters more than the growth rate itself.

Does trimming make hair grow faster?
No. Trimming does not change how fast hair grows from the follicle. It removes length, which this calculator subtracts every month. What trims can do is remove split ends before they travel up the strand and cause more breakage — which can protect your retention. See our hair growth guide for the evidence.

Should I measure natural hair stretched or shrunken?
Length levels like APL and BSL are always judged on stretched hair. If you measure your curls as they dry, choose “Shrunken” and enter your shrinkage — the calculator converts it to stretched length before doing the math.

How do I find my own growth rate?
Pick one section (the nape or crown works well), stretch it and measure from scalp to ends on the same day each month. If you relax your hair, measure the new growth at the roots before a touch-up and divide by the number of months since the last one.

Can hair really grow an inch a month?
That is well above the averages reported in research. Claims of an inch a month usually come from measuring differently (for example shrunken one month and stretched the next) or from marketing. Treat products that promise it with caution.

Sources

Last data update:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Robbins CR. Chemical and Physical Behavior of Human Hair. 5th ed. Springer; 2012. Reference text on hair structure, surfactants, conditioning agents, protein, heat and chemical treatments.

How we research and update pages: editorial policy. Spotted an error? Tell us.

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