Fatigue Severity Scale (FSS) Calculator
The Fatigue Severity Scale (FSS) is a validated 9-item questionnaire measuring how much fatigue affects your daily life. Rate each statement 1–7 based on the past week; a mean score ≥ 4 indicates clinically significant fatigue.
Score ≥ 4: clinically significant fatigue
- 1
Sum of 9 item ratings
4 + 4 + 4 + 4 + 4 + 4 + 4 + 4 + 4 = 36 - 2
FSS mean score
36 ÷ 9 = 4The mean of all 9 ratings; ≥ 4 indicates clinically significant fatigue.
How does this calculator work?
Rate 9 fatigue-impact statements from 1 to 7; the FSS score is the mean. Score ≥ 4 = clinically significant fatigue (Krupp et al. 1989 threshold). Validated in MS, ME-CFS, lupus and many other conditions. Scores 4–5 = mild, 5–6 = moderate, 6–7 = severe fatigue impact on daily life.
Formula
How this is calculated
The Fatigue Severity Scale was developed by Krupp et al. in 1989 as a brief, reliable self-report measure of fatigue severity and its functional impact. It consists of nine statements about fatigue — covering motivation, physical capacity, and the interference of fatigue with work and social life. Each statement is rated on a 7-point Likert scale from 1 (strongly disagree) to 7 (strongly agree) based on experience during the past week.
The FSS score is simply the mean of the nine item scores. Scores below 4 are generally considered not clinically significant. A score of 4 or above indicates clinically meaningful fatigue; many studies use 4 or 5 as the cut-off for significant impairment. The FSS was originally validated in patients with multiple sclerosis and lupus, but it has since been applied across many conditions including chronic fatigue syndrome/ME-CFS, Parkinson's disease, stroke, depression, and long COVID.
This calculator is intended as a screening and tracking tool. It does not replace clinical assessment. If you score above the threshold, discuss the result with a qualified healthcare provider, as fatigue may have treatable underlying causes.
Frequently asked questions
A mean FSS score of 4 or above is the validated threshold for clinically significant fatigue, as established by Krupp et al. (1989). Scores of 5–7 indicate more severe impact of fatigue on daily functioning.
The FSS was originally validated in multiple sclerosis and lupus. It is now widely used in chronic fatigue syndrome (ME-CFS), Parkinson's disease, cancer fatigue, stroke rehabilitation, depression, and long COVID research and clinical practice.
Unlike single-item fatigue ratings, the FSS measures fatigue in functional terms — how it affects motivation, physical ability, work, and social life. The Modified Fatigue Impact Scale (MFIS) and Chalder Fatigue Scale are alternatives; the FSS is the most widely used 9-item version.
Also known as
TG we-Calculate Editorial Team. (2026). Fatigue Severity Scale (FSS) Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/fatigue-severity-scale-calculator
TG we-Calculate Editorial Team. "Fatigue Severity Scale (FSS) Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/fatigue-severity-scale-calculator.
TG we-Calculate Editorial Team, "Fatigue Severity Scale (FSS) Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/fatigue-severity-scale-calculator
@misc{wecalculate_fatigue_severity_scale_calculator, title = {Fatigue Severity Scale (FSS) Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/fatigue-severity-scale-calculator}}, year = {2026}, note = {TG we-Calculate} }
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