BASDAI Calculator — Ankylosing Spondylitis Disease Activity
Quantify disease activity in ankylosing spondylitis (axial spondyloarthritis) with the validated BASDAI questionnaire. Enter scores for fatigue, spinal pain, peripheral joint pain, enthesitis and morning stiffness to get a 0–10 index — a score of 4 or above suggests active disease.
0 = no disease activity · 10 = maximal disease activity
- 1
Mean morning stiffness (Q5 + Q6) ÷ 2
(2 + 1) ÷ 2 = 1.5Q5 (severity) and Q6 (duration) are averaged before combining with other domains. - 2
Sum of five domains
3 + 3 + 2 + 2 + 1.5 = 11.5 - 3
BASDAI score
11.5 ÷ 5 = 2.3
How does this calculator work?
BASDAI = (Fatigue + Spinal pain + Peripheral joint pain + Enthesitis + mean(Morning stiffness severity, duration)) ÷ 5, on a 0–10 scale. A score ≥ 4.0 signals active ankylosing spondylitis that warrants clinical review. Rate all six questions for the past week on a 0 (none) to 10 (worst) scale.
Formula
How this is calculated
The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) was developed by Garrett et al. (1994) and is among the most widely used patient-reported outcome measures for axial spondyloarthritis. It comprises six questions covering five domains: fatigue (Q1), axial pain (Q2), peripheral joint pain and swelling (Q3), enthesitis — pain at tendon/ligament insertions (Q4), and morning stiffness assessed both for severity (Q5) and duration (Q6). Each question is answered on a 0–10 visual analogue or numeric scale.
Q5 and Q6 are averaged first (mean stiffness = (Q5 + Q6) / 2), and the resulting five values — Q1, Q2, Q3, Q4, and mean stiffness — are summed and divided by 5 to give the final BASDAI score. A score of ≥ 4.0 out of 10 is the conventional threshold used in most national guidelines to indicate active disease that may warrant consideration of biological therapy (e.g. TNF inhibitors or IL-17 inhibitors), though the threshold and treatment criteria vary by country and guideline version.
The BASDAI is sensitive to change and is used both at baseline and serially to monitor treatment response. BASDAI50 — a 50% improvement or ≥ 2-unit decrease — is a common clinical trial endpoint. Limitations: it is entirely patient-reported, captures disease activity over the past week, and does not include objective biomarkers such as CRP. It should be interpreted alongside clinical examination, imaging and inflammatory markers.
Frequently asked questions
A BASDAI ≥ 4.0 is the widely used threshold for active disease in ankylosing spondylitis. Most European and US guidelines require a BASDAI ≥ 4 (together with failure of conventional therapy and elevated CRP or MRI evidence) before initiating biological treatment. Always confirm with the specific national guideline in use.
Q6 asks the patient to rate how long morning stiffness lasts, mapped to a 0–10 scale where 0 = no stiffness and 10 = 2 hours or longer. A common linear mapping is: score = minutes of stiffness / 12, capped at 10. Instruct patients to rate based on stiffness lasting from waking until it improves.
No. BASDAI is entirely patient-reported; ASDAS (Ankylosing Spondylitis Disease Activity Score) combines patient-reported items with an objective lab marker (CRP or ESR). ASDAS is generally preferred where lab values are available; BASDAI remains important for monitoring patient-perceived disease burden and in settings where labs are not routinely obtained.
TG we-Calculate Editorial Team. (2026). BASDAI Calculator — Ankylosing Spondylitis Disease Activity [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/basdai-calculator
TG we-Calculate Editorial Team. "BASDAI Calculator — Ankylosing Spondylitis Disease Activity." TG we-Calculate. 2026. https://we-calculate.com/calculator/basdai-calculator.
TG we-Calculate Editorial Team, "BASDAI Calculator — Ankylosing Spondylitis Disease Activity," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/basdai-calculator
@misc{wecalculate_basdai_calculator, title = {BASDAI Calculator — Ankylosing Spondylitis Disease Activity}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/basdai-calculator}}, year = {2026}, note = {TG we-Calculate} }
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