About the Fatigue Severity Scale (FSS)
The Fatigue Severity Scale is a validated, 9-item self-report questionnaire developed by Krupp, LaRocca, Muir-Nash, and Steinberg (1989) to quantify how fatigue affects a person's motivation, exercise tolerance, and daily physical, occupational, and social functioning. It was originally developed for multiple sclerosis and systemic lupus erythematosus and is now widely used in research and clinical practice for chronic fatigue syndrome, fibromyalgia, Parkinson's disease, cancer-related fatigue, and general fatigue tracking. Each statement is rated on a 1-to-7 scale, from strongly disagree to strongly agree.
How the score is calculated
Rate agreement with each of the nine statements from 1 (strongly disagree) to 7 (strongly agree). The FSS score is the arithmetic mean of the nine ratings: mean = (sum of all 9 items) ÷ 9, giving a value between 1.0 and 7.0. Some clinicians instead report the raw sum of the nine items, which ranges from 9 to 63 — dividing that sum by 9 always returns the same mean score, so the two formats carry identical information.
Interpreting your score
A mean score of 4.0 or higher is the threshold most often cited in the literature as indicating clinically significant fatigue. For context, published studies typically report average FSS scores of about 2.3-3.0 in healthy adults without a fatiguing illness, about 4.8 in people with multiple sclerosis, and about 5.5 in people with chronic fatigue syndrome. Because fatigue can fluctuate day to day, the FSS is often repeated over time to track change rather than relied on as a single snapshot — a rising trend is generally more informative than any one score.
This calculator is an educational self-assessment tool, not a diagnostic instrument. It does not replace evaluation by a physician, and persistent or worsening fatigue should be discussed with a healthcare provider, since it can have many underlying causes (sleep disorders, anemia, thyroid dysfunction, depression, medication side effects, or a neurological or autoimmune condition).