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Most henna and indigo guides give you fixed times: "leave henna on for 2 hours, then indigo for 1 hour." These numbers are reasonable starting points, but they assume the same target shade, the same grey percentage, and the same hair texture for every person reading. In practice, someone with fine hair and 20% grey targeting warm brown needs very different timing from someone with thick hair and 70% grey targeting black. Using the wrong timing produces results that are too light, too patchy, or too red before the indigo step compensates. The calculator below and the explanation that follows gives you the personalised answer.

The timing calculator

Answer three questions to get your personalised henna and indigo leave-on times.

If the calculator does not load, use the henna and indigo shade finder for shade guidance and refer to the timing tables in this article.

Why timing varies: the three factors explained

Target shade is the primary determinant of both henna and indigo time. Auburn and copper red shades require henna only and no indigo. The red-orange pigment from henna alone creates these warm tones, and adding indigo shifts the result toward brown. For warm brown through to black, both steps are needed, and the depth of target shade determines how long each step runs. Black requires the longest henna time to build the deepest possible base, and the longest indigo time to fully neutralise the red-orange base into a true dark colour. Each shade increment between warm brown and black adds roughly 30 to 45 minutes to the indigo step and 30 minutes to the henna step.

Grey percentage affects how long both steps need to run. Grey and white hair is structurally different from pigmented hair: it has no cortical melanin, a more open cuticle structure, and a different protein composition. These structural differences make grey hair more receptive to henna initially (it absorbs the orange pigment very readily and vividly) but also means it can be more resistant to indigo's bonding to particularly for people with resistant grey, sometimes called glassy or silvery grey, where the cuticle is more compacted. Higher grey percentages generally require longer contact times for both steps to achieve full, even coverage. People with over 50% grey frequently find that the same timing that worked for a friend with 20% grey produces lighter or patchier results because their grey strands need more processing time.

Hair texture modifies the timing that shade and grey percentage determine. Fine hair has a thinner cuticle and fewer cortical layers, which means dye molecules penetrate more quickly. Fine hair processes henna in less time than coarse hair would for the same shade result, and similarly absorbs indigo faster. Coarse or thick hair has a more tightly bound cuticle and more cortical mass for the dye to penetrate. It requires more contact time to achieve the same depth of colour. For very coarse or resistant hair, insufficient contact time is the most common reason results look lighter than expected even after following standard guidelines.

The most common timing mistakes

Letting the paste dry completely. The most widespread mistake in henna application is waiting for the paste to dry and crack before rinsing. Dry paste draws moisture from the hair shaft, which weakens the hair and in some cases reduces colour uptake in the final stage of processing. The paste should be removed while it is still slightly pliable and damp. This is why covering the hair with plastic wrap or a shower cap during the processing time is important: it keeps the paste moist and prevents evaporative drying.

Leaving indigo paste sitting before applying. Indigo is an unstable dye that begins to oxidise the moment it is mixed with water. Once mixed, the active dye molecule is released from the plant material and begins reacting with oxygen in the air. After about 20 to 30 minutes, a significant proportion of the available dye has already reacted with air rather than with your hair. Mixing indigo paste 30 minutes before you plan to start applying it, which is how some guides instruct, wastes the most potent part of the dye before it ever contacts the hair. Mix immediately before applying and work quickly through each section.

Rinsing the henna step with shampoo before applying indigo. Henna creates a slightly acidic, slightly sticky surface on the hair shaft that indigo bonds to. Shampooing between the two steps strips this surface and makes indigo bonding significantly less effective. Rinse henna out thoroughly with water only, gently work the paste out with conditioner if needed, but do not shampoo until after the full 48-hour post-indigo window.

Not saturating coarse hair thoroughly. Coarse hair with high density can be difficult to saturate through to the scalp in every section. Thin sections during application and work the paste through from root to mid-length before covering with the next section. Uneven application is a common cause of patchy results that gets attributed to timing when it is actually a coverage issue.

The 48-hour rule and why it matters

After you rinse out the indigo, the colour you see is not the final colour. Both henna and indigo continue to oxidise after rinsing, and this post-rinse oxidation is responsible for a significant part of the final depth and evenness of the result. Henna typically appears bright orange-red immediately after rinsing and darkens noticeably over 24 to 48 hours. Indigo appears greenish-black immediately after rinsing (which can be alarming) and deepens to its true colour during the same window.

Washing with shampoo during this 48-hour oxidation window disrupts the process. Shampoo surfactants strip some of the loosely bonded dye molecules from the hair surface before they have fully fixed. The result is a lighter, less settled final colour than the same timing would produce with the full 48-hour wait. Most people who describe henna and indigo as "too light" or "not lasting" are washing their hair within 24 hours of the final step. Simply extending the wait to 48 hours resolves this complaint in the majority of cases.

During the 48-hour window, rinse the hair with cool water only if it feels uncomfortable. Keep the hair loose if possible and avoid excessive heat. The colour will visibly change and deepen during this period.

Frequently asked questions

The bottom line

Henna and indigo timing is not one fixed answer to it is the intersection of your target shade, your grey percentage, and your hair texture. The calculator above gives you personalised timings for both steps. The rest comes down to three practices that determine the final result more than timing does: keeping the paste moist during processing, mixing indigo fresh and applying it immediately, and waiting the full 48 hours before shampooing. Follow those three rules alongside the right timing and henna and indigo consistently produce the results people expect from them.