How long should permanent hair colour process?

Permanent colour typically processes for 25-45 minutes. Fine hair may develop in 25-30 minutes while coarse hair needs 35-45 minutes. Always follow manufacturer instructions. Previously coloured or damaged hair should be checked earlier and may need reduced processing time to prevent over-processing.

What affects chemical processing time?

Processing time is affected by hair type (fine processes faster than coarse), hair condition (damaged hair is more porous and processes faster), previous chemical treatments, ambient temperature (warmth speeds processing), and the specific product formulation. Always perform a strand test to determine exact timing for each client.

How often should I check bleach development?

Bleach should be checked every 5 minutes throughout processing. Place a small amount on the back of a card and wipe off to see the true underlying colour. Bleach continues to lift until rinsed, so remove it slightly before reaching the target shade. Maximum processing time for bleach is typically 45 minutes.

Should processing time be reduced for damaged hair?

Yes, damaged or previously over-processed hair has higher porosity and will absorb chemicals faster. Reduce processing time by 5-10 minutes and check development frequently. A strand test is essential for damaged hair to assess both timing and potential for further damage before full application.

CutCalcs

Chemical Processing Calculator — Safe Processing Times

Calculate safe processing times for colour, bleach and chemical services.

Service Type

Hair Type

Hair Condition

Previous Chemical Treatment

How We Calculate This

This calculator estimates safe chemical processing times by starting with standard processing ranges for each service type, then adjusting for hair type, condition and previous chemical history.

The formula

Processing time = Base range ± Hair type adjustment ± Condition adjustment ± Previous chemical adjustment

Fine hair: -5 minutes from base
Coarse hair: +5 minutes to base
Poor condition: -5 minutes (more porous)
Previous bleach/perm: -5 minutes safety reduction

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always perform a strand test before chemical services.