Tools

Bell CFIDS Disability Scale

Functional Capacity Rating 0–100

The Bell CFIDS Disability Scale is a functional capacity rating developed by Dr David Bell, a clinician and researcher who spent decades working with ME/CFS patients. It provides a single score from 0 to 100 that describes your overall level of functioning and activity limitation, where 100 represents no symptoms and full normal activity, and 0 represents severe symptoms with the patient bedridden and unable to care for themselves.

Unlike multi-item questionnaires, the Bell scale works by asking you to select the description that best matches your current level of functioning. This makes it very quick to complete and easy to understand. It is widely referenced in ME/CFS patient communities and advocacy literature, and is sometimes used informally alongside more formal instruments like the FSS.

The Bell scale is particularly useful as a simple, repeatable snapshot of functional status. Because it takes only a minute to complete, it lends itself to regular tracking. Many people with post-viral conditions use it weekly or monthly to maintain a record of their overall trajectory. For a much more detailed profile of what specific activities cost you, see the FUNCAP questionnaire. For the standard long COVID 0–4 grading, see the PCFS scale.

This is a free, interactive version. Select the description that best fits your current situation and see your score immediately. No sign-up or email is required.

This is not a diagnostic tool. Your score is a self-assessed measure of functional capacity and does not constitute a clinical diagnosis. Discuss your results with your doctor. Based on: Bell DS. The measurement of disability. In: The Doctor's Guide to Chronic Fatigue Syndrome. 2nd ed. Perseus Books; 1995. p. 119–31.

Select the description that best matches your current overall level of functioning:

Understanding your Bell scale score

What the score measures

It rates your overall level of functioning from 0 to 100 in steps of 10. Each step describes symptoms at rest and with activity, how much of a normal level of activity you manage, and how much work you could do. 100 means no symptoms and full activity; 0 means bedridden all the time and unable to care for yourself.

Dr David Bell published the scale in 1995, in The Doctor's Guide to Chronic Fatigue Syndrome. It is a set of descriptions rather than a questionnaire: you pick the one that fits best. It is widely used in ME/CFS clinics and research, including as an outcome in at least one current drug trial (NCT07724834), but we have not found a published study of its measurement properties.

Score bands

No. Each of its 11 steps is its own description, so there are no separate bands. The descriptions give activity as a share of what would be expected: close to 90% at 70, 70 to 90% at 60, about 70% at 50, 50 to 70% at 40, about 50% at 30 and 30 to 50% at 20. From 30 down, they describe being mostly confined to the house; at 10 and 0, bedridden.

A score of 40 describes moderate symptoms at rest and moderate to severe symptoms with activity, overall activity at 50 to 70% of what would be expected, not being confined to the house, and being able to do light or desk work for 3 to 4 hours a day with rest periods.

What a change in score means

No minimal important change has been published for the Bell scale. Because it moves in steps of 10, one step is the smallest change it can record. Function in ME/CFS often varies from week to week, so a change is more convincing when it holds over several weeks than when it appears once.

What it does not measure

No. It is a single overall rating of function, not a diagnostic test. It does not show which activities cost you most, how long crashes after exertion last, or which symptoms dominate.

For a profile of what specific activities cost you, the FUNCAP questionnaire covers 27 activities in eight groups. The post-exertional malaise questionnaire looks at crashes after effort, and the PCFS scale is the standard functional grading in long COVID research. Our post-exertional malaise explainer covers why activity limits work the way they do.

Taking this to your GP or consultant

Bring your score, the date, and the description you chose, since the words carry more information than the number. A trend over months is more useful than a single score. ME/CFS specialists are likely to know the Bell scale; a GP may not, so read out the description rather than relying on the number. For work or disability assessments, pair it with a FUNCAP, which records limits activity by activity. See also preparing for a GP appointment.

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