Hair Growth Calculator
Reviewed by
Steven P., FAAD
Board-certified dermatologist
Updated on
Reviewed for accuracy
Table of Contents
Hair Growth Calculator
Estimate your growth timeline based on your habits
Measurement Units
Current Length
Your Goal
Growth Rate
Breakage
Trims
Start Date (Optional)
Your Results
Net growth is zero or negative
- Try reducing trim frequency or amount
- Lower your breakage assumptions
- Select a higher growth rate if applicable
Time to Reach Your Target
Make It More Accurate
- Breakage depends on hair health, styling, and chemical treatments.
- Frequent trims keep ends healthy but slow length progress.
- Track your actual growth for 3 months to find your personal rate.
Educational only. Individual growth varies based on genetics, health, and care routine.
How to Use This Hair Growth Calculator
Quick Answer — How to Calculate Hair Growth
Multiply your monthly growth rate by the number of months, then subtract estimated breakage and trim losses. The average rate is 0.5 inches (1.25 cm) per month. The calculator above handles all of this automatically — just fill in your inputs and hit Calculate.
0.5"
Average growth per month
6"
Average growth per year
2–6 yrs
Typical anagen phase duration
~85%
Follicles actively growing at any time
Hair Growth Rates: What's Normal?
Scalp hair grows during the active anagen phase at an average of around 0.5 inches per month — but this varies considerably between individuals. Knowing where you fall is the single most important input for an accurate estimate.
Slow Grower
0.3 in/mo
≈3.6 in · ≈9 cm per year
Often linked to nutritional deficiencies, thyroid issues, high stress, or older age. Use the custom rate field if you're consistently measuring below 0.4 in/mo.
Average
0.5 in/mo
≈6 in · ≈15 cm per year
The most cited figure in dermatology literature. A safe baseline if you haven't measured your personal rate yet.
Fast Grower
0.7 in/mo
≈8.4 in · ≈21 cm per year
More common in younger adults with optimal nutrition. Asian hair types tend to grow fastest on average; tightly coiled hair tends to grow slowest.
The Three Phases of the Hair Growth Cycle
Every follicle cycles independently through three phases. Understanding them explains why length can stall even when your scalp is healthy:
- Anagen (Growth phase): Lasts 2–6 years per cycle. The only phase where hair actively grows at ~0.5 in/month. About 85–90% of your follicles are here at any given time.
- Catagen (Transition phase): Lasts 2–3 weeks. Growth stops and the follicle shrinks. Only 1–3% of follicles are in this stage simultaneously.
- Telogen (Resting phase): Lasts 3–4 months before the hair sheds and the cycle restarts. Normally 10–15% of follicles rest at once. When this percentage spikes sharply — due to stress, illness, or nutritional disruption — the result is telogen effluvium.
Hair Growth Chart: How Much Will My Hair Grow?
The table below shows projected growth at slow, average, and fast rates across the most commonly asked timeframes. These are gross growth figures — your net retained length after breakage and trims will be lower. Use the calculator above for a net figure specific to your inputs.
| Timeframe | Slow (0.3 in/mo) | Average (0.5 in/mo) | Fast (0.7 in/mo) | Avg in cm |
|---|---|---|---|---|
| 1 month | 0.3 in | 0.5 in | 0.7 in | ~1.3 cm |
| 2 months | 0.6 in | 1.0 in | 1.4 in | ~2.5 cm |
| 3 months | 0.9 in | 1.5 in | 2.1 in | ~3.8 cm |
| 6 months | 1.8 in | 3.0 in | 4.2 in | ~7.6 cm |
| 9 months | 2.7 in | 4.5 in | 6.3 in | ~11.4 cm |
| 12 months | 3.6 in | 6.0 in | 8.4 in | ~15.2 cm |
| 18 months | 5.4 in | 9.0 in | 12.6 in | ~22.9 cm |
| 24 months | 7.2 in | 12.0 in | 16.8 in | ~30.5 cm |
*Gross growth only. Net retention after 10% breakage and quarterly ½-inch trims averages 4–4.5 inches per year at the average rate.
Hair Length Benchmarks
Use this alongside the calculator to set a realistic target. Times are approximate from a 12-inch (shoulder-length) starting point at an average growth rate with minimal trims.
| Length Name | Approx. Inches | Approx. cm | Avg. Time from Shoulder (12 in) |
|---|---|---|---|
| Ear length | 6–8 in | 15–20 cm | — |
| Chin / Bob | 8–10 in | 20–25 cm | — |
| Shoulder length | ~12 in | ~30 cm | Baseline |
| Armpit length (APL) | 15–16 in | 38–41 cm | ~6–8 months |
| Mid-back length (MBL) | 18–20 in | 46–51 cm | ~12–16 months |
| Bra-strap (BSL) | 22–24 in | 56–61 cm | ~18–24 months |
| Waist length | 26–28 in | 66–71 cm | ~24–30 months |
| Hip length | 30–34 in | 76–86 cm | ~3–4 years |
*Approximate at average 0.5 in/month with minimal breakage and no trims.
What Affects How Fast Your Hair Grows?
Your genetic growth rate ceiling cannot be exceeded. But many people are growing below their maximum potential due to correctable factors. These are the ones that matter most:
Protein & Iron
Hair is almost entirely keratin — a protein — and requires iron for follicle metabolism. Low protein and low ferritin are the most commonly missed causes of slow growth and excess shedding. Get a ferritin test specifically — it's not included in a standard blood panel.
Thyroid Function
Both hypothyroidism and hyperthyroidism directly reduce growth rate and cause diffuse shedding. If growth seems unusually slow despite good nutrition, a TSH + free T4 panel is a logical next step.
Vitamin D & Zinc
Deficiencies in vitamin D and zinc can both impair growth rate and trigger shedding. Only supplement what you're actually deficient in — over-supplementing vitamin A, for example, can itself cause hair loss.
Stress
Chronic high stress prematurely pushes follicles into the resting phase, triggering telogen effluvium. Stress reduction has measurable downstream effects on the anagen phase and shedding rate.
Breakage
Hair can grow at 0.5 in/month while net length stays flat because breakage removes as much length as the follicle produces. Reducing heat damage, chemical treatments, and mechanical stress is often more impactful than any supplement — which is exactly why the breakage field in the calculator matters so much.
Scalp Health
Chronic seborrheic dermatitis, scalp inflammation, or product build-up can impair follicle function over time. A consistent scalp care routine creates the optimal environment for steady growth.
Genetics & Hair Type
Anagen phase duration is largely inherited and sets your terminal length ceiling. Asian hair tends to grow fastest (~0.6 in/mo), Caucasian hair averages ~0.5 in/mo, and tightly coiled hair tends to grow more slowly (~0.3 in/mo) — though curl pattern also affects how much length is retained.
Age & Hormones
Growth rate peaks in the 20s and gradually declines as anagen phase shortens with age. Postpartum hormonal shifts, perimenopause, and thyroid changes can all temporarily alter the rate — update your custom rate periodically to keep the calculator accurate.
Using This Calculator During Telogen Effluvium Recovery
📋 Important for Anyone Recovering From TE
After a telogen effluvium episode, many follicles re-enter the growth phase simultaneously — which is why recovery can look and feel like rapid regrowth. However, the per-follicle growth rate does not change. What changes is the number of follicles actively growing at once.
The calculator is most useful once shedding has stopped or nearly stopped, which typically happens within 6 months of the triggering event for acute TE. During active heavy shedding, breakage and shed losses can make net growth zero or negative regardless of growth rate.
Realistic Regrowth Milestones After TE
The short regrowth hairs visible during recovery start from the scalp surface and need the full growth timeline to blend in — this is why it takes 12–18 months to notice meaningful density recovery even after shedding stops.
- 6 months after shedding stops: New hairs average approximately 3 inches. Visible as a halo of shorter hair at the scalp, but not yet blending.
- 12 months: New hairs reach approximately 6 inches — beginning to blend into shoulder-length or shorter hair.
- 18–24 months: For most people with medium-length hair, this is when they genuinely feel density has returned.
What Is Terminal Hair Length?
Terminal hair length is the maximum length your hair can reach before it naturally sheds at the end of its anagen (growth) phase. It is genetically determined by how long your anagen phase lasts — typically between 2 and 6 years per follicle — and cannot be exceeded by any product or supplement.
The math is simple: if your anagen phase lasts 4 years (48 months) and you grow at 0.5 inches per month, your terminal length is approximately 24 inches. A 6-year anagen phase at the same rate yields around 36 inches. Use this to sanity-check the target you enter in the calculator — if your target is close to or above your likely terminal length, the actual timeline may exceed what the calculator projects.
Signs You May Be Near Terminal Length
- Hair hasn't grown past a certain length for over 6 months despite good care and no trims
- The ends are consistently very fine, wispy, and noticeably older-looking than growth near the scalp
- Hairs consistently shed at the same length rather than breaking off mid-shaft
Frequently Asked Questions
How do I calculate hair growth?
Use the formula: (Target Length − Current Length) ÷ Net Monthly Growth Rate = Months to Goal. Net monthly growth is your gross rate multiplied by (1 − breakage %), minus any monthly trim loss. At the average rate of 0.5 in/mo with 10% breakage and no trims, net monthly growth is 0.45 in/mo. The calculator above handles all of this automatically once you fill in your inputs.
How much will my hair grow in 2 months?
At the average growth rate of 0.5 inches per month, your hair will grow approximately 1 inch (2.5 cm) in 2 months before breakage. Slow growers (0.3 in/mo) can expect about 0.6 inches; fast growers (0.7 in/mo) may see up to 1.4 inches. After accounting for 10% typical breakage, net retained length at 2 months is roughly 0.9 inches for most people. Two months is also a useful tracking window — measure at the start and end to calculate your personal growth rate for the custom field in the calculator.
How much will my hair grow in 3 months?
At the average rate of 0.5 in/mo, hair grows approximately 1.5 inches (3.8 cm) in 3 months before breakage. Slow growers average 0.9 inches; fast growers can see up to 2.1 inches gross. Three months is the ideal window to establish your personal growth rate — track at the same scalp point monthly, divide total growth by 3, and enter it as the custom rate above.
How much will my hair grow in 5 months?
At the average rate of 0.5 in/mo, you'll grow approximately 2.5 inches (6.35 cm) in 5 months gross. Slow growers (0.3 in/mo) will see about 1.5 inches; fast growers (0.7 in/mo) up to 3.5 inches. Net retention after 10% breakage and no trims averages around 2.25 inches over that period.
How much will my hair grow in a year?
The average person grows approximately 6 inches (15 cm) of hair per year. After accounting for 10% breakage and quarterly trims of half an inch each, net annual length retention drops to roughly 4–4.5 inches for most people. This is why reaching waist length takes several years even with genuinely healthy hair — set your target in the calculator for a specific personalised timeline.
What is a hair terminal length calculator?
A terminal length calculator estimates the maximum length your hair can reach based on your anagen phase duration and monthly growth rate. The formula is: Terminal Length = Anagen Duration (months) × Monthly Growth Rate. For example, a 4-year anagen phase (48 months) at 0.5 in/mo gives a terminal length of approximately 24 inches. You can approximate this using the calculator above by entering a very long target and checking whether the projected timeline seems biologically plausible for your anagen phase length.
Does hair grow faster after telogen effluvium?
Not in terms of per-follicle rate — that stays at approximately 0.5 in/month. But after a telogen effluvium episode, a large cohort of follicles re-enter the growth phase simultaneously, creating the impression of faster or denser regrowth. Correcting iron deficiency and protein intake can restore growth to its genetic potential if those were suppressing it. Full guide: how to support regrowth after TE.
Does trimming make hair grow faster?
No — trimming does not change the rate of growth at the follicle. Growth happens at the root, not the ends. What trims do is remove split ends before they travel up the shaft and cause breakage higher up, which improves net length retention. The calculator accounts for this trade-off: a small regular trim with low breakage often produces better net growth than skipping trims entirely while accumulating high breakage.
How accurate is this hair growth estimator?
The calculator is mathematically precise for the inputs you provide. The biggest accuracy driver is your growth rate input — using your personally measured rate (tracked over 2–3 months) rather than the average preset significantly improves real-world accuracy. The results show a ±15% range to reflect normal individual biological variation. Treat the midpoint as a realistic estimate and the range as your honest window.
What slows hair growth the most?
The biggest correctable suppressors of hair growth are iron and ferritin deficiency, thyroid dysfunction, inadequate dietary protein, and high chronic stress. Genetics and age also affect rate but cannot be changed. Breakage — from heat, chemicals, and mechanical damage — can additionally mask growth entirely by removing length as fast as it grows. See our top 10 treatments for TE for an evidence-ranked list of interventions.
Related Resources
Medically Reviewed
Reviewed for accuracy against authoritative clinical sources and peer-reviewed dermatology references. Educational content only — not a substitute for professional medical advice.
Reviewed by: Steven P., FAAD — Board-certified dermatologist
Updated: March 2026
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Read our Editorial Policy →Reviewed by
Steven P., FAAD
Board-certified dermatologist
Updated on
Reviewed for accuracy