Beauty Calculators
Root touch-up timing.
Roots show when new growth reaches the length you are willing to see. Enter your growth rate and that length to get weeks until your next colour, relaxer or perm touch-up, a due date and what a year of touch-ups costs. Runs in your browser.
Your regrowth
When it is due
Fill the form and press Calculate.
Worked example
Your hair grows 12 mm a month and you touch up when regrowth reaches 24 mm. 24 / 12 = 2 months, which is about 61 days or 8.7 weeks, so 6 touch-ups a year. At $100 each that is $600 a year. If your last service was 1 January, the next is due about 3 March.
How it works
months until due = regrowth you accept / growth per month; weeks = months x 365.25 / 12 / 7; touch-ups a year = 12 / months. Regrowth today = growth rate x months since your last service. The weekly table is rate x time.
Growth rate. The page starts from the commonly quoted average of about half an inch (1.25 cm, 12.5 mm) a month (American Academy of Dermatology, how hair grows). It varies by person, season and age. To measure yours, mark the length of regrowth at your root line and measure again after a month.
Relaxers, perms and keratin. The timing here is only about how much new growth is showing. Chemical services have their own product limits and your stylist may recommend a longer wait to protect the hair at the line of demarcation, so check the product directions before shortening the gap. Not medical advice: do a patch test before colouring, and stop and see a doctor if you get a reaction.
Sources and basis (checked 2026-10-05): arithmetic on the figures you enter; average growth rate from the American Academy of Dermatology page above; 1 in = 25.4 mm exactly.
FAQ
How often should I touch up my roots?
When the regrowth reaches the length you are willing to see. At about 12.5 mm (half an inch) of growth a month, 15 mm shows after about 5 weeks and 25 mm after about 9 weeks.
How many weeks between hair colour appointments?
Divide the regrowth you accept by your growth per month. Many people colour every 4 to 8 weeks, but it depends on how different your natural colour is from your dye.
How often should I touch up a relaxer?
It depends on your growth and your stylist. This tool tells you when a set length of new growth appears; chemical services also have product-specific limits, so follow the directions and your stylist.
How fast does hair grow?
About half an inch (1.25 cm or 12.5 mm) a month on average. Everyone differs, so measure your own for a better estimate.
Does the due date change if I enter a different regrowth length?
Yes. A smaller accepted regrowth brings the due date forward, and a larger one pushes it back.