Fatigue Severity Scale Calculator
Complete the validated 9-question Fatigue Severity Scale (FSS) questionnaire to assess your fatigue level and receive evidence-based recommendations.
Rate each statement on a scale from 1 (strongly disagree) to 7 (strongly agree) based on your experience over the past week.
Fatigue Severity Scale Calculator
Complete the validated 9-question Fatigue Severity Scale (FSS) questionnaire to assess your fatigue level and receive evidence-based recommendations.
FSS score interpretation examples
These examples illustrate how different response patterns map to FSS scores.
| Response pattern | FSS score | Interpretation |
|---|---|---|
| All 9 responses rated 2 (Disagree) | FSS = 2.0 | Well below the clinical threshold; fatigue has minimal impact on daily life. |
| All 9 responses rated 4 (Neutral) | FSS = 4.0 | At the clinical threshold; further evaluation recommended to identify contributing causes. |
| All 9 responses rated 5 (Slightly Agree) | FSS = 5.0 | Severe fatigue territory; significant functional impairment, prompt medical review advised. |
| Mix: questions 1–4 rated 3, questions 5–9 rated 6 | FSS ≈ 4.67 | Above clinical threshold; fatigue interferes with physical, occupational, and social activities. |
About the Fatigue Severity Scale
The Fatigue Severity Scale (FSS) is a nine-item self-report questionnaire designed to assess the impact of fatigue on everyday functioning. It was developed by Lauren Krupp and colleagues in 1989, initially to measure fatigue in patients with multiple sclerosis (MS) and systemic lupus erythematosus (SLE). Since its publication it has been translated into numerous languages and validated across a wide range of conditions including chronic fatigue syndrome (ME/CFS), rheumatoid arthritis, sleep disorders, cancer-related fatigue, depression, and healthy populations.
Each of the nine items describes a statement about fatigue and its effects — from motivation and exercise tolerance to occupational and social functioning. Respondents rate each statement on a seven-point Likert scale ranging from 1 (strongly disagree) to 7 (strongly agree), with the instruction to rate each item relative to their experience over the past week. The FSS score is computed as the mean of all nine responses, yielding a continuous value between 1.0 and 7.0.
The widely accepted clinical threshold for significant fatigue is an FSS score of 4.0 or above. In population studies of healthy adults, average FSS scores typically fall between 2.3 and 3.3, whereas scores in clinical populations with fatigue-associated conditions routinely exceed 4.0 and often approach 5.0 to 6.0. In clinical research, an FSS score ≥ 4 is frequently used as an inclusion criterion for fatigue treatment studies, and a reduction of 0.5 to 1.0 points is considered a clinically meaningful improvement.
The psychometric properties of the FSS are well established. Internal consistency is high (Cronbach's alpha typically 0.88–0.96), test-retest reliability is strong (intraclass correlation coefficients of 0.84–0.90), and the scale demonstrates good discriminant validity — distinguishing fatigued patients from non-fatigued controls with sensitivity and specificity generally above 80%.
Fatigue is a non-specific symptom that can arise from many causes: inadequate or disrupted sleep, anemia, thyroid dysfunction, diabetes, heart failure, chronic infections, autoimmune diseases, mood disorders such as depression and anxiety, medications, and deconditioning. Because the FSS does not identify the cause of fatigue, a score at or above the clinical threshold is a prompt to investigate further rather than a diagnosis in itself. This calculator is an educational screening aid and is not a substitute for clinical assessment by a qualified healthcare professional.
How to use the Fatigue Severity Scale calculator
- Read each of the nine statements carefully and think about your experience over the past week.
- For each statement, select the number from 1 (strongly disagree) to 7 (strongly agree) that best reflects your experience.
- Answer all nine questions — the FSS score is the mean of all responses and requires a complete data set.
- Click Calculate FSS Score to see your average score, fatigue level, and clinical interpretation.
- If your score is at or above 4.0, consider discussing the result with your healthcare provider to explore potential underlying causes.
Fatigue Severity Scale FAQ
What FSS score indicates significant fatigue?
An FSS score of 4.0 or above is the established clinical threshold for significant fatigue. This cutoff has been validated across multiple studies and populations as the point at which fatigue begins to materially interfere with daily functioning. Scores below 4.0 are generally considered within the non-clinical range.
How is the FSS score calculated?
The FSS score is simply the arithmetic mean of the nine item ratings. Add the values for all nine responses and divide by nine. For example, if the sum of all ratings is 36, the FSS score is 4.0. Higher scores indicate more severe fatigue impact.
What conditions is the FSS used for?
The FSS was originally developed for multiple sclerosis and lupus but has been validated for use in chronic fatigue syndrome, rheumatoid arthritis, sleep disorders, depression, cancer-related fatigue, Parkinson's disease, and many other conditions. It is also used in healthy populations to establish normative baseline data.
Is the FSS the same as other fatigue measures?
The FSS is one of several validated fatigue questionnaires. Others include the Multidimensional Fatigue Inventory (MFI), the Brief Fatigue Inventory (BFI), and the FACIT-Fatigue scale. The FSS is particularly valued for its brevity, strong psychometric properties, and widespread validation across diverse clinical populations.
Can fatigue be treated if my FSS score is high?
Yes, but treatment depends entirely on the underlying cause. Fatigue secondary to anemia responds to iron or B12 supplementation; fatigue from hypothyroidism responds to thyroid hormone replacement; depression-related fatigue often improves with therapy or antidepressants. Lifestyle interventions such as structured exercise, cognitive-behavioral therapy (CBT), and improved sleep hygiene benefit many people regardless of cause.
How often should I complete the FSS?
The FSS is typically administered at a clinical baseline and then repeated at 4–12 week intervals to monitor treatment response or track changes over time. In research settings, a change of approximately 0.5–1.0 points is considered clinically meaningful. Patients managing chronic fatigue conditions often find monthly self-assessments helpful for spotting trends.