Hair color longevity calculator

It usually lasts until the regrowth shows, more than a set number of weeks: hair grows about 1 cm a month according to the NIH StatPearls, and what decides when the touch-up is due is how visible the regrowth is against the colored hair. In between, permanent color also loses intensity with washing. The weeks this calculator gives are a Blendsor estimate of how long the color holds up with the routine you enter in the calculator, not of when regrowth will show, and not a manufacturer figure.

Because it's held in the fiber less firmly than permanent color, it fades with washing: each wash takes some of it, and when a line's fact sheet gives a number of washes, that's the ceiling. Demi-permanents wash out too: Redken US presents Shades EQ as a demi-permanent toner and says it lasts up to 28 washes. That's the best case: with porous hair or a lot of sun, color dulls before it reaches that ceiling, and with daily washing you reach it in fewer weeks. The starting weeks in this calculator are a Blendsor estimate, not taken from any fact sheet: with your line's sheet in hand, go by the sheet.

Yes. Hard water minerals (calcium, magnesium, iron) deposit on the cuticle and accelerate pigment oxidation. The result is dull color that tends to shift brassy or greenish. A shower filter or chelating treatment every 2-3 weeks reduces the impact.

Sulfates (SLS, SLES) are strong detergents, and what they clean away includes color. Switching to a sulfate-free or color-specific shampoo is the simplest change to ask for. What we haven't found is a comparable number for how much longer it makes color last: the ones on the bottles we've read aren't measured the same way.

It is the most important factor alongside color type. High-porosity hair absorbs pigment quickly but releases it just as fast. Low-porosity hair takes longer to absorb but retains better. This is why a porosity assessment before coloring is key to adjusting the formula.

Yes. Light fades color through photodegradation: it breaks down the structure of the artificial pigment, and that wear adds to what washing takes. Covering the hair or using a hair sunscreen with a UV filter in the sunniest months is the practical way to reduce it.

The calculator makes an indicative estimate from the color type and 6 general factors: the starting weeks and the weight of each factor are Blendsor estimates, not manufacturer figures or study results. Blendsor works with the brand and line the salon uses, each client's history and the diagnosis, and suggests the formula and the aftercare for that case.