Hair Growth Calculator — Time to Reach Target Length
Human hair grows on average 1.27 cm (0.5 inches) per month, but growth varies considerably by genetics, age, nutrition and hair health. Enter your current hair length, your target length and your personal growth rate to see how many months — or years — it will take, plus a month-by-month growth curve.
cm
cm
cm/month
≈ 2 years • 103 weeks
- 1
Length to grow
35 − 5 cm = 30 cm - 2
Months to target length
30 cm ÷ 1.27 cm/month = 23.6
How does this calculator work?
Hair grows ~1.27 cm/month (0.5 in/month) on average. Months to grow = (target − current length) ÷ monthly growth rate. Enter your current length (cm), target length (cm) and growth rate (cm/month) to get the time in months and years, plus a month-by-month projection curve.
Formula
How this is calculated
The growth of a single hair strand follows an anagen (active growth) phase during which the follicle adds roughly 0.3–0.5 mm of hair per day — equivalent to about 1–1.7 cm per month. The commonly cited average of 1.27 cm/month (0.5 in/month) is derived from studies on scalp hair in populations of mixed ethnicity; individual rates vary from roughly 0.6 cm/month at the low end to 1.7 cm/month at the high end. Hair on other parts of the body grows more slowly and has a much shorter anagen phase.
This calculator treats hair growth as linear over time: total growth = rate × time, so time = (target − current) ÷ rate. This is the standard assumption for planning; in practice, mechanical damage (heat styling, bleaching, environmental factors) and natural shedding mean that the net retained length over time can be somewhat less than the follicle output, particularly for longer hair. Regular trims to remove split ends typically reduce split-end breakage and may allow more length to be retained per unit of time despite removing some length periodically.
Factors known to influence growth rate include nutritional status (biotin, iron, protein, zinc deficiencies slow growth), age (rate typically declines from the mid-30s onward), thyroid function, stress levels, and scalp health. The monthly growth rate input is editable — if you have tracked your own growth rate, enter it for a personalized estimate.
Frequently asked questions
The widely cited average for scalp hair is about 1.27 cm (0.5 inches) per month, or roughly 15 cm (6 inches) per year. However, research shows individual rates range from 0.6 to 1.7 cm/month. East Asian hair tends to grow the fastest; African hair tends to grow the slowest in terms of strand length due to its helical shape (though follicle output per unit time is similar). The default of 1.27 cm/month is a reasonable population midpoint.
No product is proven to meaningfully increase the follicle's intrinsic growth rate beyond its genetic maximum. However, correcting underlying deficiencies (low iron, low ferritin, low protein, hypothyroidism, or biotin deficiency) can restore a rate slowed by those factors. Minimising mechanical damage — reducing heat use, using wide-tooth combs, gentle handling, and protective styles — allows more of the hair that grows to be retained at the ends.
Regular trims remove split ends that would otherwise travel up the shaft and cause breakage, which can actually increase the net length retained over time. If you trim 1–2 cm every 8–12 weeks, subtract that from the net length gained; for example, at a 1.27 cm/month growth rate and a 1.5 cm trim every 3 months, net gain is 1.27 × 3 − 1.5 = 2.31 cm per quarter. Adjust the effective growth rate in this calculator accordingly.
Also known as
TG we-Calculate Editorial Team. (2026). Hair Growth Calculator — Time to Reach Target Length [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/hair-growth-calculator
TG we-Calculate Editorial Team. "Hair Growth Calculator — Time to Reach Target Length." TG we-Calculate. 2026. https://we-calculate.com/calculator/hair-growth-calculator.
TG we-Calculate Editorial Team, "Hair Growth Calculator — Time to Reach Target Length," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/hair-growth-calculator
@misc{wecalculate_hair_growth_calculator, title = {Hair Growth Calculator — Time to Reach Target Length}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/hair-growth-calculator}}, year = {2026}, note = {TG we-Calculate} }
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