Project how long your hair will grow. This free hair growth calculator estimates length over time or time to a target length, in cm or inches, using slow, average or fast growth rates.
Scalp hair grows about 1-1.5 cm (roughly half an inch) a month on average. Add your current length to project total length or to see how long it’ll take to reach a target.
Hair grows from the follicle at a fairly steady rate during its growing (anagen) phase. Genetics, age, health, nutrition and hormones all affect speed — these are averages, and trims don’t change how fast hair grows.
How the Hair Growth Calculator Works
This tool projects hair length over time, or estimates how long it will take to reach a target length, using a simple average monthly growth rate. It works either direction: forward from a starting length over a set number of months, or backward from a target length to find the time needed.
Formula: Length after time = Current length + (Growth rate × Months). Time to a length = (Target length − Current length) ÷ Growth rate. The growth rate is a fixed monthly value: slow (1.0 cm / 0.4 in), average (1.25 cm / 0.5 in), fast (1.5 cm / 0.6 in), or a custom value you enter.
- Growth rate — length gained per month, chosen from slow/average/fast presets or a custom figure, in cm or inches.
- Current length — your starting hair length (optional; treated as 0 if left blank).
- Months — used in “length after time” mode: how many months you’re projecting forward.
- Target length — used in “time to a length” mode: the length you want to reach.
Example Scenarios
| Growth Rate | Current Length | Time | Total Length After Time |
|---|---|---|---|
| Slow (1.0 cm/mo) | 0 cm | 6 months | 6 cm |
| Average (1.25 cm/mo) | 10 cm | 12 months | 25 cm |
| Fast (1.5 cm/mo) | 5 cm | 8 months | 17 cm |
| Average (1.25 cm/mo) | 20 cm | 24 months | 50 cm |
| Slow (1.0 cm/mo) | 15 cm | 3 months | 18 cm |
| Fast (1.5 cm/mo) | 0 cm | 20 months | 30 cm |
Getting Realistic Estimates from a Hair Growth Calculator
A hair growth calculator multiplies a growth rate by time, so the rate you choose matters most. Scalp hair often grows somewhere around 1 to 1.5 cm a month, but individuals vary.
- Measure your own rate: note the length of regrowth at a colour line or parting, wait a month, and measure again.
- Account for trims. A hair growth calculator shows raw growth, so if you trim 1 cm every two months, subtract that from the result.
Rerun the hair growth calculator with your measured rate for a far more personal answer.
Long hair also runs into a natural limit. Each follicle grows for a set phase before resting and shedding. A hair growth calculator assumes growth simply continues, so very long targets may exceed what your own cycle allows.
Sudden shedding, patches of hair loss or very slow regrowth are worth raising with a doctor or dermatologist. The human hair growth article on Wikipedia explains the anagen, catagen and telogen phases behind any hair growth calculator estimate.
Hair Growth Calculator FAQ
How fast does hair actually grow per month on average?
Scalp hair typically grows around 1 to 1.5 cm (roughly 0.4-0.6 inches) per month on average, though this varies by individual. This calculator uses slow, average and fast presets within that general range, or you can enter your own observed rate as a custom value.Does cutting or trimming hair make it grow faster?
No — trims remove length from the ends but don’t change the rate at which hair grows from the follicle. Growth speed is determined by factors at the scalp, like genetics and hormones, not by how often the ends are cut.Why might my hair be growing slower than the “average” rate here?
Individual growth speed is affected by genetics, age, overall health, nutrition, and hormonal factors, so real-world results commonly fall outside a single average figure. If your growth consistently seems very slow, it may be worth discussing with a doctor or dermatologist.How do I estimate how long it’ll take to reach a certain length?
Switch the calculator to “time to a length,” enter your current length and your target length, and pick a growth rate. It divides the difference between target and current length by the monthly rate to estimate the number of months needed.Do the cm and inch growth rate presets convert to the same value?
Not exactly — each preset stores its own typical cm and inch figure (for example, average is listed as 1.25 cm or 0.5 in per month) rather than converting one unit into the other, since these are rounded reference values rather than precise unit conversions.Does hair growth slow down as you get older?
Many people do notice hair growth gradually slowing with age, alongside other changes in hair texture and thickness, though the degree varies widely from person to person. This calculator uses a steady monthly rate and doesn’t adjust for age-related changes.Related Calculators
Because hair is largely made of protein, some people find it helpful to check the protein intake calculator alongside a growth projection, and low iron is another commonly discussed factor worth checking with the iron intake calculator. General hydration habits, viewable with the daily water intake calculator, round out the bigger picture of overall wellness that growth rate alone doesn’t capture.