The Kirby-Desai Scale: Predicting Sessions Before the First Pulse

“How many sessions will it take?” is the first question every client asks, and guessing at the answer is how specialists lose their trust three months later. There is a structured way to answer it.

The Kirby–Desai scale scores six factors, sums them, and the total gives you the predicted number of sessions. Its validation shows a correlation of R=0.757 against the real number of sessions performed — which makes it one of the more accurate clinical instruments available in this field.

The six factors

1. Fitzpatrick skin phototype

Points	Phototype
1	I–II
2	III
3	IV
4	V–VI

2. Location of the tattoo

Points	Location
1	Head, neck
2	Upper trunk
3	Upper limbs
4	Lower limbs

3. Colour of the tattoo

Points	Colour
1	Black
2	Blue / dark
3	Red / orange
4	Green / yellow and similar

4. Pigment density

Points	Density
1	Minimal (amateur or faint work)
2	Moderate
3	Dense
4	Very dense (professional, multi-layered)

5. Scarring in the tattooed area

Points	Condition
0	No scarring
1	Minimal changes
2	Moderate scarring
3	Pronounced scarring

6. Layering (cover-ups and retouching)

Points	Situation
0	Primary tattoo, no retouching
1	Minor retouching
2	Substantial cover-up

Reading the total

Total score	Predicted sessions
4–5	~4–5 sessions (favourable)
6–8	~6–8 sessions
9–12	~9–12 sessions
13–18	~13–18 sessions
19–26+	20+ sessions (unfavourable)

A worked example

• Phototype II — 1 point
• Location: forearm — 3 points
• Colour: black with red — 2 points (averaged)
• Density: moderate — 2 points
• Scarring: none — 0 points
• Cover-up: none — 0 points

Total: 8 points → approximately 8 sessions.

What the scale does not know

Use it honestly, which means knowing its blind spots:

• It does not account for your equipment — a compact device and a stationary system are not interchangeable
• It does not account for lifestyle: smoking, immune status
• It does not account for the ink’s actual composition, which is usually unknown
• R=0.757 is a good correlation, but roughly a quarter of the variability remains unexplained

So the working formula is: score + correction for your equipment + correction for lifestyle = the prognosis you give.

At the consultation

Score all six factors, add them up, and give the client a range — “probably 8 to 12 sessions” — then say plainly that this is a prognosis and not a guarantee. Where the score is high, 15 and above, tell them honestly that the course will be long, and consider whether a stationary laser is the better referral.

Clients do not lose trust because a course took ten sessions. They lose it because someone promised three.