CDAI Calculator (Crohn’s Disease Activity Index)

Understanding the CDAI calculator — concept and principle

This calculator works out the Crohn's Disease Activity Index (CDAI) from eight weighted items: a seven-day symptom diary, complications, anti-diarrhoea medicine, abdominal mass, haematocrit and body weight. It gives the score, the activity band and the size of the main parts. Gastroenterology teams, trial staff and patients tracking symptoms use it.

Diary + signs + labs — with the default inputs: CDAI 218.

How it is calculated

Liquid or very soft stools over 7 days × 2
Sum of daily abdominal pain ratings (0–3) × 5
Sum of daily well-being ratings (0–4) × 7
Complication groups × 20; anti-diarrhoea medicine × 30; abdominal mass (0, 2 or 5) × 10
(47 − haematocrit for men, or 42 − haematocrit for women) × 6
Percentage below standard weight = (1 − weight ÷ standard weight) × 100
Bands: under 150 remission; 150–219 mild; 220–450 moderate; over 450 severe

The principle

Best and colleagues (1976) built the CDAI for clinical trials by finding which observations best matched doctors' overall judgement of disease activity, and weighting them accordingly. Symptoms carry most of the weight, with smaller contributions from anaemia (low haematocrit) and weight loss. Trials define response as a fall of 70 or 100 points. Because the index relies heavily on symptoms, it can be high in irritable bowel symptoms without active inflammation.

Worked example

Defaults: 20 stools, pain sum 7, well-being sum 10, 1 complication group, no anti-diarrhoea medicine, no mass, man, haematocrit 40, weight 62 kg, standard 70 kg.

Diary part = 2 × 20 + 5 × 7 + 7 × 10 = 145.
Complications = 1 × 20 = 20; medicine and mass = 0.
Haematocrit part = (47 − 40) × 6 = 42.
Weight part = (1 − 62 ÷ 70) × 100 = 11.4.
CDAI = 145 + 20 + 42 + 11.4 = 218: Mild (150–219).

Each point is the calculator re-run with only “Standard (ideal) weight for height (kg)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Standard (ideal) weight for height (kg)	CDAI score
17.5	-47
35	130
52.5	189
70	218
87.5	236
105	248
140	263

How to read the result

Where does your result fall?

This score sits just below the moderate band. Track it over time with the same diary method; changes of 70–100 points are what trials treat as meaningful. Endoscopy, blood and stool tests show inflammation more directly.

Common mistakes

Filling in the diary from memory instead of daily.
Using the wrong haematocrit constant for sex.
Entering a standard weight that is not from a height table.
Treating a high score as proof of inflammation.

Keep in mind: Not a diagnosis. Treatment decisions are made with your gastroenterology team.

Frequently asked questions

What CDAI score means remission?

Under 150.

What is a clinically meaningful change?

Trials commonly use a fall of 70 or 100 points as response.

Why is haematocrit included?

Anaemia is common in active Crohn's disease and adds information beyond symptoms.

Sources: Best WR, Becktel JM, Singleton JW, Kern F, "Development of a Crohn's disease activity index", Gastroenterology 1976;70(3):439–444 · Takeda MLN0002 protocol, ClinicalTrials.gov NCT02038920, Table 9.a

Checked 9 Nov 2026. Best WR, Becktel JM, Singleton JW, Kern F, “Development of a Crohn’s disease activity index”, Gastroenterology 1976;70(3):439–444 — items and multipliers as tabulated in the Takeda MLN0002 protocol (ClinicalTrials.gov NCT02038920, Table 9.a); remission under 150 and 220–450 moderate–severe range as used in that protocol.

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