CDAI Calculator — Crohn's Disease Activity Index
Calculate the Crohn's Disease Activity Index (CDAI) — the original validated score from Best et al. 1976 — using 7-day symptom diaries, lab values and physical findings. Scores below 150 indicate remission.
Antidiarrheal drug use
Abdominal mass
Sex
%
kg
kg
Disease activity: Remission
- 1
Hematocrit deviation × 6
6 × (reference Hct − 40) = 42Negative if measured Hct exceeds the sex-specific reference (47% male, 42% female). - 2
Weight deviation × 1
(1 − 70 ÷ 70) × 100 = 0Negative if current weight exceeds standard weight. - 3
CDAI score (sum of all components)
10 + 25 + 49 + 20 + 0 + 0 + 42 + 0 = 146
How does this calculator work?
The CDAI sums eight weighted variables from a 7-day symptom diary plus labs and a physical exam: CDAI = 2×stools + 5×pain + 7×wellbeing + 20×features + 30×antidiarrheal + 10×mass + 6×(reference Hct − measured Hct) + weight deviation. Scores <150 = remission, 150–219 = mild, 220–450 = moderate, >450 = severe Crohn's disease.
Formula
How this is calculated
The Crohn's Disease Activity Index (CDAI) was published by Best et al. in 1976 and remains a benchmark endpoint in Crohn's disease clinical trials, though it has largely been supplemented by endoscopic and biomarker measures in clinical practice. It combines eight variables collected over a 7-day period, each weighted by its contribution to disease burden.
The two largest contributors are typically stool frequency (multiplied by 2) and general well-being (multiplied by 7), reflecting their strong impact on quality of life. The hematocrit component uses sex-specific reference values (47% for males, 42% for females) and becomes negative if hematocrit is above the reference, which can lower the total score. The weight component is also signed: being underweight (below standard weight) adds to the score, while being overweight subtracts from it.
Limitations of the CDAI include its reliance on subjective symptom diaries, the complexity of the weight component (standard weight is not clearly defined), and its poor correlation with objective inflammation markers such as C-reactive protein or endoscopy findings. A score below 150 defines remission in most clinical trials; 150–219 is mild, 220–450 is moderate, and above 450 is severe.
Frequently asked questions
A CDAI score below 150 is defined as clinical remission. A decrease of 70 or more points is often used as a response threshold in clinical trials, and a decrease of 100 points defines clinical response in many studies.
The six features are: (1) arthritis or arthralgia, (2) iritis or uveitis, (3) skin or mouth lesions — erythema nodosum, pyoderma gangrenosum, or aphthous stomatitis, (4) anal fissure, fistula or abscess, (5) other fistula, (6) fever above 37.8°C. Each feature present scores 1, so the maximum for this component is 6 (multiplied by 20 = 120 points).
The CDAI remains the primary endpoint in many clinical trials but is less common in routine clinical care. The Harvey-Bradshaw Index (a simplified version requiring no diary) and objective measures such as C-reactive protein, fecal calprotectin, and endoscopy are increasingly preferred. The CDAI score alone does not reflect mucosal healing.
TG we-Calculate Editorial Team. (2026). CDAI Calculator — Crohn's Disease Activity Index [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/cdai-calculator
TG we-Calculate Editorial Team. "CDAI Calculator — Crohn's Disease Activity Index." TG we-Calculate. 2026. https://we-calculate.com/calculator/cdai-calculator.
TG we-Calculate Editorial Team, "CDAI Calculator — Crohn's Disease Activity Index," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/cdai-calculator
@misc{wecalculate_cdai_calculator, title = {CDAI Calculator — Crohn's Disease Activity Index}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/cdai-calculator}}, year = {2026}, note = {TG we-Calculate} }
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