Medical AINIH Stroke Scale (NIHSS) severity calculator
A standardised 15-item neurological examination that grades acute stroke severity from 0 to 42. It is the common language for stroke trials and care: it helps gauge severity, informs reperfusion and triage decisions, and lets a deficit be tracked reproducibly over time.
How to measure each input
- Examine in order and score what you see
- Administer items in the standard sequence and record the patient's first effort. Do not go back and change a score, and do not coach the patient.
- Untestable items (the 9 convention)
- Limb items 5 and 6 and dysarthria (item 10) allow an untestable designation for amputation, joint fusion, or intubation. Untestable items are recorded but are not added to the total, so the maximum scorable total is reduced.
- Coma scoring
- A comatose patient (LOC item 1a = 3) scores at the impaired end on most subsequent items: for example language item 9 is scored 3 and sensory item 8 is scored 2.
- Certification matters
- The scale is most reliable when performed by a trained, certified examiner. Inter-rater variability is highest for facial palsy, ataxia, and dysarthria.
Interpretation
| Band | Meaning |
|---|---|
| 0, no stroke symptoms | No measurable neurological deficit on the scale. A score of 0 does not exclude stroke, especially posterior-circulation events that the NIHSS underweights. |
| 1 to 4, minor stroke | Minor deficit. Many of these patients still have disabling symptoms (for example isolated aphasia or hemianopia), so reperfusion is considered on the specific deficit, not the number alone. |
| 5 to 15, moderate stroke | Moderate deficit. This range commonly prompts consideration of reperfusion therapy and is associated with higher hospital resource use. |
| 16 to 20, moderate to severe stroke | Moderate to severe deficit, with higher risk of poor outcome and of haemorrhagic transformation. Arrange urgent stroke-team and neuroimaging review. |
| 21 to 42, severe stroke | Severe deficit, associated with large infarcts, high mortality, and high disability. Manage with the stroke team and consider airway and neurocritical-care needs. |
Pitfalls, exclusions and caveats
- The NIHSS underweights posterior-circulation strokes. Disabling brainstem or cerebellar deficits (vertigo, diplopia, ataxia, dysphagia) can produce a low total, so a low score does not mean a benign stroke.
- It is right-hemisphere biased: dominant-hemisphere (usually left) strokes score higher because language is heavily weighted, while right-hemisphere neglect contributes fewer points for a similar infarct volume.
- A single score is a snapshot. Fluctuation, extension, or early reocclusion can change the picture quickly, so reassess and trend rather than rely on one measurement.
- The score grades deficit, not eligibility for treatment. Reperfusion decisions weigh time from onset, imaging, the specific disabling deficit, and contraindications, not the NIHSS number alone.
- Reliability falls without examiner training and certification, particularly for ataxia, facial palsy, and dysarthria.
- It does not assess consciousness or airway adequacy comprehensively; pair it with vital signs and, where relevant, the Glasgow Coma Scale.
Sum of 15 items: 1a LOC (0 to 3) + 1b LOC questions (0 to 2) + 1c LOC commands (0 to 2) + 2 best gaze (0 to 2) + 3 visual fields (0 to 3) + 4 facial palsy (0 to 3) + 5a left arm (0 to 4) + 5b right arm (0 to 4) + 6a left leg (0 to 4) + 6b right leg (0 to 4) + 7 limb ataxia (0 to 2) + 8 sensory (0 to 2) + 9 best language (0 to 3) + 10 dysarthria (0 to 2) + 11 extinction and inattention (0 to 2). Total 0 to 42.The NIH Stroke Scale was developed by Brott et al. (1989) and is maintained by NINDS. This implementation is an educational tool and is not affiliated with the original authors or any guideline body. Use a certified examiner and the official scale for clinical care.
Frequently asked
What NIHSS score counts as a severe stroke?
Common bands are 0 (no symptoms), 1 to 4 (minor), 5 to 15 (moderate), 16 to 20 (moderate to severe), and 21 to 42 (severe). These bands describe deficit, not a treatment threshold, and exact cut-offs vary between sources.
Can a stroke be serious with a low NIHSS score?
Yes. The NIHSS underweights posterior-circulation and right-hemisphere strokes, so a disabling deficit such as isolated severe vertigo, hemianopia, or aphasia can carry a low total. Decisions should rest on the specific deficit and imaging, not the number alone.
How are untestable items handled?
Limb motor items (5 and 6) and dysarthria (item 10) allow an untestable designation for amputation, joint fusion, or intubation. Untestable items are documented but not added to the total, which lowers the maximum achievable score for that exam.
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