Scalp hair grows about 1–1.5 cm a month on average – roughly 15 cm (6 in) a year – though genetics, age, health and nutrition all play a part. Regular trims remove split ends but also some length, so they slow how fast hair appears to grow.
How to use the Hair Growth Calculator
- Current length
- Target length
- Growth rate per month
- Length lost to trims
- Months to project
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter your current length, your target length, your growth rate (or keep the average) and how much length trims remove.
Tips
- Use the amounts printed on the product (ml, sheets, applications) where available.
- Count everyone in the household who shares the product.
- Buy a little extra so you never run out unexpectedly.
- Small daily habits add up – check the yearly figures for the real impact.
Common mistakes to avoid
- Forgetting that hot water costs energy as well as water.
- Underestimating how much sunscreen a full application needs.
- Comparing pack prices without checking the size of each pack.
Inputs explained
| Field | What to enter |
|---|---|
| Current length | Units: in, cm |
| Target length | Units: in, cm |
| Growth rate per month | Units: in, cm, mm |
| Length lost to trims | In % |
| Months to project | A number |
What each result means
- Months to reach target = max([Target length] – [Current length], 0)÷([Growth rate per month]×(1 – [Length lost to trims]÷100))
- Date estimate (from today) = today() + [Months to reach target]×30.44
- Length after the projected months = [Current length] + [Growth rate per month]×(1 – [Length lost to trims]÷100)×[Months to project]
- Net growth per year = [Growth rate per month]×(1 – [Length lost to trims]÷100)×12
Example values
How the main result changes when Current length changes and everything else stays at the example values above:
| Current length (in) | Months to reach target |
|---|---|
| 5 | 24.4 |
| 7.5 | 18.9 |
| 10 | 13.3 |
| 12.5 | 7.8 |
| 15 | 2.2 |
| 20 | 0 |
Formula
Length gained = growth rate × months (≈ 0.5 in or 1.25 cm per month)Months needed = (target length − current length) ÷ (growth rate × (1 − trim loss))Worked example
Inputs — Current length: 10 in; Target length: 16 in; Growth rate per month: 0.5 in; Length lost to trims: 10 %; Months to project: 12.
Results — Months to reach target = 13.3; Date estimate (from today) = Sat, December 4, 2027; Length after the projected months = 15.4 in; Net growth per year = 5.4 in.
Frequently asked questions
How fast does hair grow?
About half an inch (1.25 cm) a month, or 6 in (15 cm) a year on average.
Do trims make hair grow faster?
No – hair grows from the root; trims keep ends healthy so length isn't lost to breakage.
How long does it take to grow hair to shoulder length?
From a short bob, often 1–2 years.
What formula does the Hair Growth Calculator use?
Length gained = growth rate × months (≈ 0.5 in or 1.25 cm per month).