Fatigue Severity Scale (FSS)
Take the validated 9-question Fatigue Severity Scale (Krupp 1989) in 60 seconds. Free, no signup, results stay in your browser. Score 1.0–7.0.
Last updated: Sources verified:
What you are about to take
The Fatigue Severity Scale (FSS) measures how much fatigue is interfering with your life — not what is causing it. Nine statements about the last week, each rated 1 (strongly disagree) to 7 (strongly agree). The score is the mean — range 1.0–7.0. About 60 seconds. No signup. The FSS was developed by Krupp, LaRocca, Muir-Nash, and Steinberg in 1989 (Archives of Neurology), validated initially in multiple sclerosis and systemic lupus, and is now the most widely used fatigue measure in neurology and primary care. Your answers stay in your browser — we never see them. Start the test below ↓
- Validated by Krupp, LaRocca, Muir-Nash, Steinberg (1989, Arch Neurol)
- Used in NICE NG206 (ME/CFS), WHO post-COVID work, and most MS / lupus cohorts
- 60 seconds, 9 statements
- Private — answers never leave your device
How the FSS is scored
You rate nine statements about fatigue over the last week, each 1 to 7. The FSS score is the mean of the nine items (not the sum — the most common scoring mistake). Range 1.0–7.0.
| Mean | Band | What the band typically means |
|---|---|---|
| < 3.0 | Low / typical | Healthy-adult range. Fatigue is not the thing limiting you. |
| 3.0–4.9 | Mild–moderate | Significant fatigue. Often reversible (sleep, iron, thyroid, B12, D, mood). GP visit within 4 weeks for a standard fatigue workup. |
| 5.0–7.0 | High / clinically significant | Krupp 1989 cutoff. Doctor visit within 1–2 weeks. Standard fatigue workup; flag long COVID or post-exertional malaise if relevant. |
FSS measures the disability, not the cause
This is the key thing to remember. A high FSS is consistent with many conditions:
- Multiple sclerosis — original Krupp 1989 validation cohort
- Systemic lupus, Sjögren”s, rheumatoid arthritis — autoimmune fatigue
- Myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) — NICE NG206 2021, which moved AWAY from graded exercise therapy
- Long COVID / post-COVID-19 condition — WHO 2021 case definition names fatigue as a core symptom
- Hypothyroidism / hyperthyroidism — straightforward to test, often missed
- Anaemia — iron-deficiency (ferritin, not just haemoglobin), B12, folate
- Obstructive sleep apnea — overlaps with the Epworth Sleepiness Scale; one of the most under-recognized causes
- Major depression — fatigue is a core somatic symptom of depression; the PHQ-9 is a sensible adjunct
- Medication side effects — beta-blockers, antihistamines, statins, antidepressants, opioids
- Lifestyle — insufficient sleep, sustained stress, dehydration, deconditioning are all common, all reversible
A high FSS does not narrow this list. It signals “this needs investigation” — and at the standard fatigue panel, primary care picks up a treatable cause in roughly 40–50% of cases (Cathébras 1992; Cornuz 2006 review).
What to ask a GP — the standard fatigue panel
| Test | What it picks up |
|---|---|
| Full blood count (CBC) | Anaemia (any kind) |
| Ferritin | Iron stores — picks up iron deficiency before haemoglobin drops |
| TSH and free T4 | Hypothyroidism, hyperthyroidism |
| Vitamin B12 | B12 deficiency (common cause of fatigue + neuropathy) |
| Vitamin D | Deficiency is widespread and contributes to fatigue |
| HbA1c or fasting glucose | Diabetes, prediabetes |
| ESR / CRP | Inflammation, autoimmune disease, chronic infection |
| Urea, electrolytes, liver function | Renal and hepatic causes |
Add: sleep apnea screening (STOP-BANG questionnaire) if you snore or wake unrefreshed. Add: post-exertional malaise screen — if fatigue worsens 24–72 hours after even small effort, mention this explicitly. PEM is specific to ME/CFS, and the management approach (pacing, not graded exercise) is the opposite of generic fatigue advice.
When this test is useful — and when it isn”t
Useful for:
- Bringing a quantified fatigue score to a GP visit instead of “I”m tired all the time”
- Tracking change over time — repeat every 2–6 weeks
- Differentiating ordinary tiredness (resolves with rest) from a fatigue pattern (persists despite rest)
Not useful for:
- Diagnosing a specific cause — that requires history, exam, and labs
- Children — the FSS is validated in adults; paediatric fatigue scales (e.g. PedsQL Multidimensional Fatigue Scale) exist for under-18s
- Acute fatigue from a single bad night or short illness — the scale is interpreted as a pattern over the last week
- Replacing a clinical assessment — it triages, it does not diagnose
A note on post-exertional malaise (PEM)
If your fatigue worsens 24–72 hours after even small physical or mental effort — disproportionate to what would be expected, lasting days — that pattern is called post-exertional malaise (PEM), and it is the cardinal feature of ME/CFS. PEM also occurs in long COVID. It is specifically NOT normal deconditioning, and the management approach is the opposite of “exercise more”. CDC and NICE (NG206 2021) both updated guidance to recommend pacing — staying within an energy envelope — rather than the graded-exercise protocols of the 1990s and 2000s. If PEM applies to you, mention it explicitly to your GP.
Related calculators
- Epworth Sleepiness Scale (ESS) — different from FSS; measures the tendency to fall asleep, not fatigue interference
- PHQ-9 depression screener — depression and fatigue overlap heavily; both worth taking
- STOP-BANG sleep apnea screen — one of the most under-diagnosed fatigue causes
- GAD-7 anxiety screener — sustained anxiety drives fatigue
Sources verified 2026-05-17
- Krupp LB, LaRocca NG, Muir-Nash J, Steinberg AD. The Fatigue Severity Scale. Application to patients with multiple sclerosis and systemic lupus erythematosus. Archives of Neurology 1989;46(10):1121–1123. (PMID 2803071)
- Lerdal A, Wahl AK, Rustøen T, Hanestad BR, Moum T. Fatigue in the general population: a translation and test of the psychometric properties of the Norwegian version of the fatigue severity scale. Scandinavian Journal of Public Health 2005;33(2):123–130. (PMID 15823973)
- National Institute for Health and Care Excellence. Myalgic encephalomyelitis (or encephalopathy) / chronic fatigue syndrome: diagnosis and management (NG206). NICE, 29 October 2021.
- World Health Organization. A clinical case definition of post COVID-19 condition by a Delphi consensus. WHO, 6 October 2021.
- Centers for Disease Control and Prevention. About ME/CFS and About Long COVID. CDC, accessed 2026-05-17.
- American Academy of Family Physicians. Fatigue: an overview. AFP 2008;78(10):1173–1179 (updated commentary).
Privacy
The FSS calculation runs entirely in your browser. Your individual answers and the calculated band never leave your device. We send one anonymous event to a privacy-respecting analytics service: your locale code and the FSS band string (for example band_high). No raw answers, no per-item data, no identifier of any kind.
Frequently asked questions
What does an FSS score of 5 mean?
An FSS mean of 5.0 sits in the high band (5.0–7.0) — the band where Krupp 1989 set the cutoff for clinically significant fatigue. It does not diagnose a specific condition. It does say that fatigue is interfering with most daily activities most of the time, and that a GP visit is warranted in the next 1–2 weeks for a standard fatigue workup: CBC, ferritin, TSH and free T4, vitamin D, vitamin B12, HbA1c, ESR/CRP.
What does an FSS score of 4 mean?
A mean of 4.0 is the mid band (3.0–4.9) — meaningful fatigue, common, often reversible. A mean ≥ 4 is the threshold used in many research studies (Krupp 1989) to flag fatigue worth investigating. The most common drivers at this level are insufficient sleep, undiagnosed iron deficiency, thyroid issues, low vitamin D/B12, mild depression, and obstructive sleep apnea. Any single one can move the mean from 4.5 to 2.5 within months when treated.
Is an FSS score under 3 normal?
Yes. A mean below 3.0 is the low/typical band, where healthy adults without a fatigue-related condition cluster. Lerdal 2005 reported population means in the 2.0–2.8 range. Low FSS does not mean unlimited energy — it means fatigue is not the thing limiting you right now.
FSS vs ESS — are these the same scale?
No. The Fatigue Severity Scale (FSS) measures fatigue — the heavy, drained feeling that interferes with daily life. The Epworth Sleepiness Scale (ESS) measures sleepiness — the tendency to actually fall asleep in low-stimulation situations like reading or sitting in a car as a passenger. Sleepiness and fatigue often overlap (sleep apnea drives both) but they are clinically distinct, and the workup differs. A high ESS pushes towards sleep apnea evaluation; a high FSS pushes towards a broad fatigue workup.
FSS vs MFI — which one is more accurate?
They measure different things. The FSS (Krupp 1989) is a 9-item single-dimensional measure of fatigue interference. The Multidimensional Fatigue Inventory (MFI-20, Smets 1995) breaks fatigue into 5 dimensions (general, physical, mental, reduced motivation, reduced activity). The FSS is shorter and used more in primary care; the MFI-20 is preferred for research where the dimension matters (e.g. distinguishing cancer-related from depression-related fatigue).
Am I more than just tired? How can I tell from this test?
Tiredness from a busy week typically resolves with one weekend of rest and produces an FSS mean around 2–3. If your mean is consistently above 4 across separate weeks, even after weekends with adequate sleep, that is the signal that something more than ordinary tiredness is going on. Repeat the test 2–4 weeks apart to separate a hard-week spike from a real fatigue pattern.
Is the FSS useful for long COVID?
Yes — and it is one of the most used scales in long COVID research. The WHO post-COVID-19 condition case definition (2021) names fatigue as one of the three core symptoms, present 3+ months after acute infection. An FSS mean ≥ 4 alongside symptoms persisting after a COVID infection is a strong signal to flag long COVID by name to a GP — some health systems have specific post-COVID pathways.
What does FSS look like in MS, lupus, and ME/CFS?
Mean FSS in MS ranges 4.5–5.5 in cohort studies (Krupp 1989 original work). Mean FSS in systemic lupus is similar, typically 4.0–5.0. Mean FSS in ME/CFS is the highest of the three, often 6.0+. None of these are unique to one condition though — a high FSS is consistent with all of them, and the differential is opened by history, exam, and labs, not by the FSS score alone.
I am tired from work — is that the same as a high FSS?
Probably not. Work-related fatigue is usually episodic and recovers with weekends or a holiday. The FSS asks about fatigue over the last week and is interpreted as a *pattern*. If you have been in a brutal sprint at work and your FSS is 4.5 this week but 2.5 in a normal week, that is reactive fatigue, not a fatigue disorder. The clinical concern is when a high FSS persists for 4+ weeks despite normal sleep and reasonable workload.
What causes high fatigue — what is the differential?
Broad but tractable. The standard differential covers: sleep (insufficient sleep, obstructive sleep apnea, restless legs), endocrine (hypo- or hyperthyroidism, diabetes, adrenal insufficiency), haematology (iron-deficiency anaemia, B12 deficiency), infection (post-viral including long COVID, mononucleosis, chronic Lyme in endemic areas), autoimmune (lupus, Sjögren's, rheumatoid arthritis, MS), psychiatric (major depression — fatigue is a core symptom), medication side effects (beta-blockers, antihistamines, statins, antidepressants, opioids), and lifestyle (sedentary, dehydration, sustained stress). A GP visit and the standard fatigue panel cover most of these in one pass.
What should I ask my GP — which blood tests?
Ask for the standard fatigue panel: full blood count (CBC) to rule out anaemia, ferritin (iron stores — not just haemoglobin), TSH and free T4 (thyroid), vitamin B12, vitamin D, HbA1c or fasting glucose, ESR or CRP (inflammation), urea and electrolytes, liver function tests. Add sleep apnea screening (e.g. STOP-BANG questionnaire) if you snore or wake unrefreshed. Add a screen for post-exertional malaise if you feel disproportionately worse 24–72 hours after activity — that pattern is specific to ME/CFS.
Is graded exercise therapy still recommended for ME/CFS?
No — and this is important. NICE NG206 (2021) explicitly moved away from graded exercise therapy as a treatment for ME/CFS, after evidence that for people with post-exertional malaise, graded exercise can cause harm. Pacing — staying within an "energy envelope" and stopping activity before symptoms flare — is the current evidence-based approach. If your fatigue worsens 24–72 hours after even small effort, mention PEM explicitly to your GP and ask about pacing.
How accurate is the FSS — does it really pick up MS-related fatigue?
The FSS is the most widely cited fatigue scale in MS research and was validated against clinical fatigue ratings in Krupp 1989. Cronbach's alpha is consistently above 0.88, test-retest reliability is high. It is not a diagnostic test — it cannot tell MS-related fatigue from lupus-related fatigue from long COVID fatigue. It tells you the magnitude of fatigue-related disability, which is what most patients and clinicians need quantified first.
Does my FSS test stay private?
Yes. The calculator runs entirely in your browser. Your individual answers never leave your device. We log one anonymous event with the FSS band (e.g. `band_high`), nothing more — no raw answers, no IP, no identifier.
Sources
- The Fatigue Severity Scale. Application to patients with multiple sclerosis and systemic lupus erythematosus — Krupp LB, LaRocca NG, Muir-Nash J, Steinberg AD — Archives of Neurology (1989) (peer reviewed, retrieved 2026-05-17)
- Fatigue in the general population: a translation and test of the psychometric properties of the Norwegian version of the fatigue severity scale — Lerdal A, Wahl AK, Rustøen T, Hanestad BR, Moum T — Scandinavian Journal of Public Health (2005) (peer reviewed, retrieved 2026-05-17)
- Myalgic encephalomyelitis / chronic fatigue syndrome: diagnosis and management (NG206) — National Institute for Health and Care Excellence (NICE) — 2021 (guideline, retrieved 2026-05-17)
- A clinical case definition of post COVID-19 condition by a Delphi consensus — World Health Organization (WHO) — 2021 (guideline, retrieved 2026-05-17)
- About ME/CFS — Centers for Disease Control and Prevention — Centers for Disease Control and Prevention (CDC) (gov health, retrieved 2026-05-17)
- About Long COVID — Centers for Disease Control and Prevention — Centers for Disease Control and Prevention (CDC) (gov health, retrieved 2026-05-17)
- Fatigue: an overview — American Academy of Family Physicians (AAFP) — Rosenthal 2008, updated commentary (medical society, retrieved 2026-05-17)