How fast does hair grow?
Healthy scalp hair grows at roughly the same pace for most people. MedlinePlus says it takes about a month for healthy hair to grow half an inch, and DermNet describes a hair shaft growing about 1 centimetre a month. Half an inch is 1.27 centimetres, so the two figures sit close together, and the calculator lets you pick either or enter your own.
That works out to roughly 15 centimetres, or six inches, in a year. It is not a promise. Rates differ from person to person, and the same person can grow a little slower or faster at different times. Treat any timeline as a rough guide, not a date to circle.
How long will it take to grow my hair?
At half an inch a month with no trims, the arithmetic is simple. A few examples:
| Grow by | At about 1.27 cm (0.5 in) a month | At about 1 cm a month |
|---|---|---|
| 5 cm (2 in) | About 4 months | About 5 months |
| 10 cm (4 in) | About 8 months | About 10 months |
| 20 cm (8 in) | About 16 months | About 20 months |
| 30 cm (12 in) | About 24 months | About 30 months |
Those numbers assume your ends do not break off as fast as your roots grow. In real life they often do, which is why so many people feel their hair is stuck at one length.
Do trims slow you down?
A trim takes off length you have already grown, so yes, every trim costs you some progress. What it does not do is change how fast hair grows. Growth happens at the root, under the skin, and cutting the ends has no effect on it. Our article on whether cutting hair makes it grow faster covers the myth in more detail.
The reason people trim while growing their hair is split ends. A split that is left alone can travel further up the strand, and then more has to come off later. Small, regular trims keep the ends healthy, so you keep more of what you grow.
The calculator subtracts your trims from your monthly growth. Taking off 1 centimetre every 12 weeks, for example, removes a little over 4 centimetres a year. If you trim more than you grow, length stays the same, and the calculator says so.
Why does my hair seem to stop growing?
There are two common reasons, and neither is that your hair has stopped growing at the root.
Breakage. If the ends break as fast as the roots grow, length stays put. Damaged hair is fragile, so it snaps more easily. The American Academy of Dermatology lists everyday habits that cause it: heat styling, bleaching and other chemical treatments, rough towel drying, brushing wet hair hard, and tight hairstyles that pull.
Your growth phase. Each hair grows for a limited time before it rests and sheds. How long that growing phase lasts sets a ceiling on how long your hair can get, and it differs between people. Our article on the hair growth cycle explains the phases.
How to keep more of the length you grow
Since growth itself is hard to speed up, the realistic goal is to lose less of it:
- Use heat less often, on a lower setting, and with a heat protectant when you do.
- Detangle gently, starting at the ends and working up, with conditioner in your hair.
- Pat hair dry with a towel instead of rubbing.
- Swap tight ponytails and buns for looser styles, and change where they sit.
- Space out chemical treatments like bleach and relaxers, and look after your hair in between.
- Trim small amounts regularly rather than a lot at once.
Our guide on how to prevent hair breakage goes into each of these.
Can anything make hair grow faster?
Nothing reliably speeds up healthy hair beyond its natural rate. Supplements help when someone is genuinely short of a nutrient, but they do not push growth past normal in people who are not. If your hair has slowed down, thinned or started falling out in a way that worries you, that is a question for a doctor rather than a calculator.
How the calculator works
You enter your length now, your goal and your trim routine. The calculator converts everything to centimetres, takes your monthly growth rate, subtracts what your trims remove each month, and divides the length still to grow by what is left. It shows the months it would take, the month you might get there, and how much length your trims cost you in a year.
The growth rates come from MedlinePlus and DermNet, linked below. The result is an estimate, not a diagnosis, and nothing you enter is saved or sent.
Track the length you keep
Length depends as much on breakage as on growth. The HairLens app reads breakage and split ends from your photos, keeps every scan so you can compare them, and builds a routine around what is actually happening to your hair.