What is the BASDAI score?

BASDAI stands for Bath Ankylosing Spondylitis Disease Activity Index. It is a validated 6-question index, each scored on a 0–10 visual analogue scale, used to measure disease activity in ankylosing spondylitis. The score is (Q1 + Q2 + Q3 + Q4 + mean(Q5, Q6)) / 5, giving a result between 0 and 10.

How is the BASDAI score calculated?

Add the first four question scores (fatigue, spinal pain, peripheral joint pain/swelling, enthesitis), then add the average of the two morning-stiffness questions (severity and duration), then divide the total by 5. This calculator does it automatically as you move the sliders.

What does a BASDAI score of 4 or higher mean?

A score of 4 or higher is the commonly used cutoff for active disease, and it is the threshold many guidelines and insurers use when considering biologic therapy. It is a screening aid, not an automatic treatment decision — your rheumatologist interprets it in context.

What is a good BASDAI score?

Lower is better. A score below 4 generally indicates low disease activity. Many treatment targets aim to bring the score under 4, and ideally as low as possible, alongside your doctor's broader clinical assessment.

How often should I check my BASDAI?

Many rheumatologists ask patients to complete BASDAI at each visit, or every few weeks when treatment changes. Tracking it over time is more useful than a single reading, because trends show whether disease activity is improving or worsening.

Why are the two morning stiffness questions averaged?

Morning stiffness severity (Q5) and duration (Q6) are averaged into a single component so that stiffness does not count double relative to the other four domains. Each of the five components — fatigue, spinal pain, peripheral pain, enthesitis, stiffness — carries equal weight.

Is BASDAI the same as BASFI or BASMI?

No. BASDAI measures disease activity (symptoms). BASFI (Bath Ankylosing Spondylitis Functional Index) measures physical function, and BASMI (Bath Ankylosing Spondylitis Metrology Index) measures spinal mobility. They are complementary instruments used together in clinical practice.

Can I use BASDAI to diagnose ankylosing spondylitis?

No. BASDAI is designed for people already diagnosed with ankylosing spondylitis (or axial spondyloarthritis) to monitor activity. It cannot diagnose the disease — diagnosis requires clinical evaluation, imaging, and laboratory work by a rheumatologist.

Does a high BASDAI automatically mean I need biologics?

Not automatically. A score of 4 or higher suggests active disease and is a common eligibility criterion for biologic therapy, but the final decision involves your full clinical picture, other test results, contraindications, and shared decision-making with your rheumatologist.

Is this BASDAI calculator free and private?

Yes. It is free, runs 100% in your browser, and none of your answers leave your device — there is no account, no tracking of your scores, and no data sent to any server.

BASDAI Calculator — Bath Ankylosing Spondylitis Disease Activity Index

The 6 BASDAI questions

Rate each over the past week, from 0 (none) to 10 (very severe).

Your BASDAI score

0.0

Low disease activity

Score < 4 suggests low disease activity.

BASDAI = (Q1 + Q2 + Q3 + Q4 + mean(Q5, Q6)) ÷ 5

Worked examples

Load a preset to see how the score is built up:

How BASDAI is interpreted

Score ≥ 4 — active disease. This is the commonly used cutoff for considering biologic therapy (per rheumatology guidelines and many reimbursement criteria).
Score < 4 — low disease activity.

The morning-stiffness component (Q5 severity and Q6 duration) counts as a single averaged item, so stiffness cannot dominate the score. Track your score over time and discuss trends with your rheumatologist.

Scope boundary

This tool measures ankylosing spondylitis disease activity (BASDAI) only. It is not a general pain scale, not a BASFI functional index, and not a BASMI mobility measure — those are separate instruments with different questions and scoring.

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The 6 BASDAI questions

Your BASDAI score

Worked examples

How BASDAI is interpreted

Frequently asked questions

Scope boundary

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