Hair Growth Calculator
If you are growing your hair to a target length, the practical question is how long it will take. This calculator answers it from three numbers you control: your current length, your target length, and your monthly growth rate. Because growth rate is highly individual and not a fixed figure, you enter your own measured rate rather than relying on an assumed average. The result is the growth still needed, the number of months at your rate, the equivalent in years, and the length you can expect after a chosen number of months.
Hair growth formula
Growth needed = target length - current length
Months to target = growth needed / monthly growth rate
Years to target = months to target / 12
Projected length = current length + monthly growth rate * months ahead
This is a simple linear model: hair gains the same amount each month at the rate you enter. Use the same length unit throughout for a correct result.
Hair growth context
- Growth rate is individual and is not a single fixed value, so you supply your own.
- The model is linear, assuming a steady rate every month.
- Trims reduce length, so factor them into your target or rate if you trim regularly.
- Any consistent unit (cm or inches) works as long as all three inputs use it.
- The projection is an estimate; track your own length over time for the most accurate rate.
Hair growth: frequently asked questions
How do I calculate how long my hair will take to grow?
Subtract your current length from your target length to get the growth needed, then divide by your monthly growth rate. If you need 10 cm more and grow 1.25 cm per month, that is 8 months. This calculator does the arithmetic and also converts the result to years.
What growth rate should I enter?
Hair growth rate varies by individual, age, and many other factors, so there is no single true figure to hardcode. Enter your own measured rate, or a value you have tracked. The default is provided only as a starting point and should be replaced with your real rate.
Why is the growth rate a user input rather than fixed?
Because it is an empirical, person-specific value. Publishing a single fixed rate would be misleading for many users. Keeping it editable means the result reflects your actual hair, not an average that may not apply to you.
Can I work in inches instead of centimetres?
Yes, as long as you use the same unit for current length, target length, and growth rate. If all three are in inches, the months and years results are still correct. Mixing units will give a wrong answer.
Is the projection linear?
This calculator assumes a steady monthly growth rate, which is a simple linear model. Real growth can vary over time and with trimming, so treat the result as an estimate based on the rate you enter.
Official sources
- National Institutes of Health, MedlinePlus: Hair problems and hair health.
- National Institute of Standards and Technology: Length unit definitions.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.