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Fatigue Severity Scale (FSS) Calculator
Measure self-reported fatigue burden with the 9-item Fatigue Severity Scale and its mean 1-to-7 score.
⚠️ Medical Disclaimer: The FSS is a screening tool for fatigue severity. Persistent unexplained fatigue should be evaluated by a healthcare provider to rule out medical causes.
Rate each statement about how fatigue has affected you during the past week (1 = strongly disagree, 7 = strongly agree):
FSS Mean Score3.9 / 7
Fatigue Severity
3.9
No Significant Fatigue
Fatigue levels within normal range
Q1
5
Q2
4
Q3
4
Q4
4
Q5
4
Q6
3
Q7
4
Q8
3
Q9
4
FSS Mean Score⧉
3.9
Total: 35 / 63
Severity⧉
No Significant Fatigue
Fatigue levels within normal range
Highest-Rated Item⧉
Q1
5 / 7 on the most strongly endorsed statement
Clinically Significant?⧉
No
Below clinical significance threshold
Items ≥5⧉
1 / 9
Number of items at or above moderate agreement
Raw Total⧉
35 / 63
The FSS is usually interpreted by mean score rather than total alone
| FSS Mean | Interpretation | Screening Use |
|---|---|---|
| <4.0 | Lower reported fatigue burden | Usually below the common clinically significant threshold |
| 4.0-4.9 | Clinically significant fatigue | Worth discussing in the broader clinical context |
| 5.0-5.9 | Higher fatigue burden | Structured follow-up and cause evaluation are often appropriate |
| 6.0-7.0 | Marked fatigue burden | High self-reported impact; interpretation still depends on the underlying condition |
| Condition | Typical FSS Mean | Prevalence of Significant Fatigue |
|---|---|---|
| Healthy controls | 2.3 ± 0.7 | 5-10% |
| Multiple sclerosis | 5.3 ± 1.2 | 75-90% |
| Systemic lupus erythematosus | 4.9 ± 1.5 | 50-80% |
| Chronic fatigue syndrome | 6.1 ± 0.8 | 100% |
| Depression | 4.5 ± 1.4 | 60-75% |
| Post-COVID syndrome | 5.1 ± 1.3 | 50-70% |
Planning notes, formulas, and examples
About the Fatigue Severity Scale (FSS) Calculator
The Fatigue Severity Scale (FSS) is a 9-item self-report questionnaire that measures how strongly fatigue affects day-to-day life. Each item is rated from 1 to 7, and the mean item score is the main output.
The FSS was originally developed and validated in adults with multiple sclerosis and systemic lupus erythematosus, and it is now used more broadly as a practical self-report fatigue measure. The key number on the page is the mean score, with 4 or higher commonly used as a threshold for clinically significant fatigue.
This page is designed as a screening and tracking aid. It does not identify the cause of fatigue and it should not be treated as a disease-specific treatment algorithm.
When This Page Helps
Fatigue is common, but it is hard to compare over time without a structured measure. The FSS helps turn a vague complaint into a repeatable score that can be tracked across visits or interventions.
It is most useful for documenting the burden of fatigue and whether it is changing, not for telling you why the fatigue is happening.
How to Use the Inputs
- Rate each of the 9 statements from 1 to 7 based on the past week.
- Review the mean score first, since that is the standard FSS output.
- Use the score as a screening and follow-up measure rather than a diagnosis.
- If the score is high, interpret it in the context of sleep, mood, medical illness, medications, and the broader clinical picture.
Formula used
FSS Mean = (Sum of all 9 item scores) / 9
Range: 1.0-7.0
Higher values indicate greater self-reported fatigue burden
Mean score >= 4 is a commonly used threshold for clinically significant fatigueExample Calculation
Result: FSS Mean 4.5 — Clinically Significant Fatigue
A mean FSS score of 4.5 is above the commonly used threshold of 4.0, suggesting meaningful self-reported fatigue burden. The next step is to interpret that result in the context of the underlying condition and possible contributors.
Tips & Best Practices
- Focus on the mean score, since that is the standard FSS output.
- Use the page to compare fatigue burden over time rather than to assign a diagnosis.
- Interpret high scores alongside sleep, mood, medication, and medical history.
- Do not overread individual items without considering the full pattern.
- Repeat the scale under similar conditions when tracking change.
- If fatigue remains unexplained, the score supports further evaluation but does not replace it.
What the FSS Is Good For
The FSS is good at summarizing how burdensome fatigue feels and whether it is interfering with ordinary life. That makes it useful in follow-up, research, and structured symptom review.
What It Is Not
It is not a cause finder, not a sleep study, and not a disease-specific management algorithm. A high score can occur in many medical and non-medical situations.
Best Use
Use the FSS as a repeatable symptom measure. Its value comes from documenting burden and change over time, not from pretending the number alone explains the fatigue.
Sources & Methodology
Last updated:
Methodology
This page applies the original Fatigue Severity Scale by averaging the nine 1-to-7 item scores into the standard mean score. The mean score is the main output because that is the conventional FSS summary used in the original validation work and later fatigue-screening studies.
The page is intended as a self-reported fatigue-burden measure rather than a cause-finding tool. A mean score of 4 or higher is a common threshold for clinically significant fatigue, but the number still has to be interpreted alongside sleep, mood, medications, chronic illness, and the broader clinical context.
Sources
- The fatigue severity scale. Application to patients with multiple sclerosis and systemic lupus erythematosus (PubMed / Archives of Neurology)
- Fatigue Severity Scale (Shirley Ryan AbilityLab) — Rehabilitation-measures summary describing score structure, common cutoff use, and measurement background.
Frequently Asked Questions
It measures self-reported fatigue burden and how strongly fatigue interferes with daily life. It does not identify the cause of fatigue.
No. A high FSS can occur in many settings and is not specific to one diagnosis.
Fatigue is a sense of exhaustion or reduced energy, while sleepiness is a tendency to fall asleep. The two can overlap, but they are not the same thing.
A mean score of 4 or higher is a commonly used threshold for clinically significant fatigue, but the interpretation still depends on the clinical setting.
Yes. That is one of its main practical uses. Repeating the scale can help show whether the fatigue burden is changing.
The standard FSS was developed for adults. Pediatric fatigue assessment usually uses other tools.
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