NIH Stroke Scale (NIHSS) Calculator
Quantitative assessment of stroke severity across 11 neurological domains. Scores range from 0 (no deficits) to 42 (maximum impairment), guiding thrombolysis eligibility, thrombectomy candidacy, and prognostication in acute ischaemic stroke.
Calculate NIH Stroke Scale
Score each domain using the best response observed. Items should be scored in order. Do not coach the patient. Record what the patient does, not what you think they can do. For untestable items (e.g., limb amputation), select “UN — Untestable” where available; these items contribute 0 to the total.
The NIHSS is a clinical assessment tool — it does not diagnose stroke or determine treatment eligibility on its own. Treatment decisions (thrombolysis, thrombectomy) require integration of the NIHSS with imaging findings, symptom onset time, patient comorbidities, and clinical judgement. A low NIHSS does not exclude large vessel occlusion or significant stroke.
Understanding the NIH Stroke Scale
The NIH Stroke Scale was developed in 1989 by Brott, Adams, and colleagues at the National Institutes of Health as a standardised, quantitative measure of stroke-related neurological deficit. It was designed for use in acute stroke clinical trials but has become the universal bedside tool for stroke severity assessment in emergency departments, stroke units, and neurocritical care settings worldwide.
The scale evaluates 11 domains (15 individually scored items) spanning consciousness, vision, motor function, sensation, language, and attention. Each item is scored on an ordinal scale from 0 (normal) to a maximum of 2–4 depending on the domain, yielding a total range of 0 to 42. Higher scores indicate greater neurological impairment.
Scale Structure
Total = Sum of all 15 items
11 domains, 15 scored items:
LOC (items 1a, 1b, 1c)
Gaze (item 2)
Visual Fields (item 3)
Facial Palsy (item 4)
Motor Arms (items 5a, 5b)
Motor Legs (items 6a, 6b)
Ataxia (item 7)
Sensory (item 8)
Language (item 9)
Dysarthria (item 10)
Extinction (item 11)
Key Treatment Thresholds
IV Alteplase (tPA):
Generally considered for NIHSS ≥ 4 within 4.5 hours of symptom onset. NIHSS < 4 may qualify if symptoms are “mild but disabling.”
Mechanical Thrombectomy:
Considered for NIHSS ≥ 6 with confirmed large vessel occlusion (LVO) on imaging. Extended window up to 24 hours with perfusion mismatch (DAWN/DEFUSE-3 criteria).
The NIHSS is weighted toward anterior circulation. The scale dedicates 7 of 15 items (and a disproportionate share of achievable points) to motor and language functions served by the middle cerebral artery territory. Posterior circulation strokes — including basilar artery occlusion — may present with devastating deficits (coma, bilateral motor loss, cranial nerve palsies) yet score deceptively low on the NIHSS. A low NIHSS does not exclude a large or dangerous stroke.
NIHSS Score Interpretation & Severity Categories
The NIHSS total is conventionally grouped into severity categories that correlate with functional outcome, mortality, and treatment decisions. These thresholds are derived from major stroke trials and registry data.
| NIHSS Score | Severity | Clinical Correlate | Typical Outcome |
|---|---|---|---|
| 0 | No stroke symptoms | Normal neurological examination | Full recovery expected; may still have completed stroke on imaging |
| 1–4 | Minor stroke | Subtle deficits: minor facial droop, mild drift, slight sensory change | ~75% achieve good outcome (mRS 0–1); consider if “disabling” |
| 5–15 | Moderate stroke | Significant deficits: hemiparesis, gaze deviation, aphasia, neglect | Variable; strong candidate for reperfusion therapy |
| 16–20 | Moderate-to-severe stroke | Dense deficits: severe hemiplegia, global aphasia, forced gaze deviation | Majority have poor outcome without treatment; higher ICH risk with tPA |
| 21–42 | Severe stroke | Severe global deficits; often obtunded or comatose | High mortality; significant disability in survivors |
NIHSS change is as important as the absolute score. An improvement of ≥ 4 points within 24 hours of treatment is considered clinically meaningful and suggests effective reperfusion. Conversely, a worsening of ≥ 4 points warrants urgent reassessment — repeat imaging to exclude haemorrhagic transformation, re-occlusion, or cerebral oedema. Serial NIHSS monitoring at 2, 24, and 72 hours post-treatment is standard practice in most stroke protocols.
NIHSS and Treatment Eligibility
| Treatment | Time Window | Typical NIHSS Threshold | Key Considerations |
|---|---|---|---|
| IV Alteplase (tPA) | 0–4.5 hours | Generally ≥ 4 | “Mild but disabling” symptoms may qualify even at NIHSS < 4 |
| IV Tenecteplase | 0–4.5 hours | Generally ≥ 4 | Emerging alternative to alteplase; single bolus dosing |
| Thrombectomy (early) | 0–6 hours | ≥ 6 with LVO | Confirmed LVO on CTA/MRA required (ICA, M1, proximal M2) |
| Thrombectomy (extended) | 6–24 hours | DAWN: ≥ 10; DEFUSE-3: ≥ 6 | Perfusion mismatch on CT/MR perfusion imaging required |
Clinical Applications & Domain-Specific Assessment
Each NIHSS domain tests specific neurological functions that localise the stroke and help predict the affected vascular territory. Understanding what each domain measures improves scoring accuracy and clinical interpretation.
The three LOC items assess arousal (1a), orientation (1b), and command-following (1c) separately, providing a more granular assessment than a single consciousness rating. Item 1a is scored by observation — note the minimum stimulation required to elicit a response. Item 1b asks two specific questions: the current month and the patient’s age. Only the initial answer counts — do not give credit for self-correction. Aphasic or intubated patients who cannot speak score 1 (not 2) if they clearly attempt to respond.
Item 1c asks two commands: open and close eyes, then grip and release the non-paretic hand. If the patient cannot use their hands (e.g., bilateral amputation), substitute another one-step command. Credit is given for unequivocal attempt even if not completed due to weakness. A patient who squeezes but cannot release due to frontal lobe dysfunction scores the attempt as correct.
- LOC 1a ≥ 2: Suggests large territory infarction, brainstem stroke, or raised intracranial pressure
- LOC 1b = 2: May reflect aphasia rather than true disorientation — note the distinction for clinical interpretation
- LOC 1c: Tests motor planning and comprehension independently of speech
This item tests horizontal eye movements only — vertical gaze abnormalities are not scored. Test voluntary gaze first (ask the patient to look left and right). If the patient cannot follow commands, use tracking of a moving target or oculocephalic manoeuvre (doll’s eyes). A score of 1 indicates a partial gaze palsy — the eyes can move past midline but do not achieve full lateral gaze. A score of 2 indicates forced deviation or complete gaze paresis that cannot be overcome by oculocephalics.
Forced eye deviation toward the side of the lesion (away from the hemiplegic side) is a classic sign of large middle cerebral artery territory infarction. In contrast, forced deviation toward the hemiplegic side (“wrong-way eyes”) may suggest a pontine lesion or thalamic haemorrhage. Isolated abducens (CN VI) nerve palsy is scored as 1, not 2, as it represents a single nerve deficit rather than cortical gaze centre involvement.
Visual fields are tested by confrontation in all four quadrants of each eye simultaneously. The examiner holds up fingers (or uses visual threat in obtunded patients) in the upper and lower quadrants of each hemifield. A score of 1 indicates an asymmetry including quadrantanopia. A score of 2 indicates complete hemianopia — blindness in one entire hemifield. A score of 3 is reserved for bilateral hemianopia, including cortical blindness.
This item is particularly important for posterior cerebral artery (PCA) strokes, which may present with isolated homonymous hemianopia and a deceptively low total NIHSS. Patients with visual field cuts may not be aware of their deficit (anosognosia), so bilateral simultaneous stimulation should be used. If the patient is blind in one eye from prior pathology, the remaining eye is tested and the result extrapolated bilaterally.
Motor testing is performed one limb at a time, starting with the non-paretic side. Arms are held at 90° if seated or 45° if supine; legs at 30° supine. The examiner should not place the limb in position and then release it — the patient must actively elevate and maintain the position. Count a full 10 seconds for arms, 5 seconds for legs.
A score of 1 (drift) means the limb does not maintain the full position for the required time but does not contact the bed. A score of 2 (some effort against gravity) means the limb falls to the bed within the time period but can partially resist gravity. A score of 3 (no effort against gravity) means the limb falls immediately. The distinction between 1 and 2 is critical and is often miscored — counting seconds aloud improves accuracy.
- Pronator drift: Subtle early sign of upper motor neuron weakness; the arm pronates as it drifts — this scores 1
- Test each limb individually: Testing bilaterally simultaneously masks subtle unilateral weakness
- “UN” for amputation or joint fusion: Document the reason and exclude from the total score
Language assessment uses standardised stimuli: the patient is asked to name common objects (pictured), read sentences aloud, and describe a complex scene (the “cookie theft” picture). Comprehension is assessed throughout the entire examination. A score of 0 indicates no aphasia. A score of 1 indicates mild-to-moderate aphasia — the patient can communicate their ideas despite some difficulty. A score of 2 indicates severe aphasia — only fragmentary communication is possible. A score of 3 indicates mute or global aphasia — no usable speech and no comprehension.
This item is heavily weighted in the NIHSS and contributes up to 3 points. Left hemisphere (dominant) MCA strokes often produce significant aphasia scores, while non-dominant hemisphere strokes may produce little or no language deficit — contributing to the well-documented right hemisphere scoring bias of the NIHSS. Importantly, dysarthria (slurred speech) is not aphasia — a patient who slurs but uses correct words and grammar scores 0 on language and receives points on item 10 (dysarthria) instead.
This item assesses for hemispatial neglect — the failure to attend to stimuli on one side of space. Test with simultaneous bilateral stimulation in visual and tactile modalities. Present visual stimuli (wiggling fingers) simultaneously in both visual fields, and touch both hands simultaneously. A patient with extinction will report only the stimulus on the intact side when both are presented together, even though they can detect each stimulus when presented individually.
Hemispatial neglect is a hallmark of non-dominant (typically right) parietal lobe lesions and is one of only two NIHSS items (along with gaze) that may capture right hemisphere stroke severity. Profound neglect with anosognosia (unawareness of deficit) carries significant prognostic implications for rehabilitation — patients who deny their hemiplegia have substantially longer recovery trajectories. Spatial neglect can also be assessed during line bisection tasks or scene description, though these are not formally part of the NIHSS.
Left MCA: Right hemiparesis, aphasia (items 9+10 high), right visual field cut, right facial weakness — typically high NIHSS (15–25+). Right MCA: Left hemiparesis, neglect (item 11), left visual field cut, left facial weakness — often lower NIHSS (10–18) despite similar infarct size due to reduced language item contribution. Posterior circulation: May present with coma, bilateral deficits, cranial nerve palsies, and ataxia yet score ≤ 5 on the NIHSS.
Special Populations & Assessment Considerations
Several clinical scenarios require careful consideration when interpreting the NIHSS. The score may over- or underestimate stroke severity depending on the population and clinical context.
“Mild but disabling” deficits may warrant treatment even at low NIHSS. A score of 2–3 that reflects isolated hand weakness in a surgeon, isolated aphasia in a lecturer, or hemianopia in a professional driver carries functional implications far beyond the numerical score. Treatment decisions should consider the functional impact of the deficit, not just the NIHSS number.
Systematic Approach to NIHSS Assessment
The NIHSS should be performed in a standardised sequence. Proper technique reduces inter-rater variability (which has been reported as ± 2–4 points) and ensures no domain is overlooked during the time-pressured acute stroke assessment.
NIHSS certification (available free at nihstrokescale.org) is recommended for all clinicians performing the assessment. Certified examiners demonstrate significantly lower inter-rater variability compared to untrained clinicians. The certification involves video-based training and examination with standardised patients.
Position the patient comfortably — typically semi-recumbent at 30–45°. Ensure adequate lighting for visual field and pupil testing. Have the standardised NIHSS picture card, reading card, and naming objects available. The entire assessment takes approximately 6–8 minutes when performed systematically. Remove any visual or auditory aids (glasses, hearing aids) only if they are not the patient’s baseline equipment — assess the patient as they normally function.
Several fundamental rules govern NIHSS scoring that are frequently violated in practice. First, score what you see, not what you think the patient can do. If a patient has aphasia and cannot answer orientation questions, they score 2 on item 1b — even if you suspect they know the answers. Second, do not coach. Give the instruction once, clearly. If the patient does not respond, repeat the instruction a maximum of one additional time. Do not rephrase, gesture, or demonstrate.
Third, score in order — the sequence matters because earlier items may influence the approach to later items (e.g., if 1a reveals coma, visual field testing method changes). Fourth, score at the first attempt — for items 1b (orientation questions), the initial response counts. Self-correction is not credited. Fifth, for untestable items (marked “UN”), explain the reason and exclude from the total — do not assign a score or estimate what it might have been.
Serial NIHSS assessment is essential for tracking stroke trajectory and detecting complications. Recommended assessment intervals vary by protocol but typically include: baseline (pre-treatment), 2 hours post-thrombolysis, then every 4–6 hours for the first 24 hours, then every shift (8–12 hours) for the first 72 hours. More frequent assessment is warranted if the patient is clinically unstable.
Document the total score, individual item scores, time of assessment, and the examiner’s identity. Note any items that changed from the prior assessment. A change of ≥ 4 points is considered clinically significant. Worsening triggers urgent reassessment including repeat neuroimaging to exclude haemorrhagic transformation (post-tPA), re-occlusion, progressive oedema, or new ischaemic event. Improvement of ≥ 8 points within 24 hours of thrombectomy suggests successful reperfusion.
Common Pitfalls & Limitations
Despite its widespread adoption, the NIHSS has well-documented limitations. Understanding these pitfalls prevents misinterpretation and inappropriate treatment decisions.
The NIHSS was primarily developed and validated in anterior circulation stroke populations. It contains no items for vertigo, diplopia, dysphagia, nystagmus, or Horner syndrome — all of which are common and often disabling posterior circulation stroke symptoms. A basilar artery occlusion causing locked-in syndrome (complete quadriplegia with preserved consciousness) may score only 10–12 on the NIHSS, grossly underrepresenting the catastrophic nature of the deficit.
Clinical impact: Patients with posterior circulation symptoms and low NIHSS scores may be inappropriately triaged as “minor stroke” and denied emergent intervention. Any patient presenting with acute vestibular symptoms, bilateral motor deficits, cranial nerve palsies, or cerebellar signs should receive emergent vascular imaging (CTA) regardless of the NIHSS score. The posterior NIHSS (pNIHSS) has been proposed but is not yet widely validated.
The NIHSS consistently underscores right hemisphere strokes relative to left hemisphere strokes of comparable size. Language items (9 and 10) contribute up to 5 points and are typically abnormal only in dominant (left) hemisphere strokes. Meanwhile, the right hemisphere’s contribution — primarily neglect (item 11, max 2 points) and gaze (item 2, max 2 points) — is underrepresented in the total score.
Clinical impact: Studies demonstrate that for a given NIHSS score, right hemisphere strokes have worse outcomes than left hemisphere strokes because the NIHSS underestimates their true severity. This can lead to under-triage and delayed treatment of right MCA occlusions. Clinicians should be aware that an NIHSS of 10 in a right hemisphere stroke may represent greater ischaemic burden than an NIHSS of 10 in a left hemisphere stroke. Consider vascular imaging liberally in right hemisphere presentations even with moderate scores.
An NIHSS of 0–4 is categorised as “minor stroke,” but this label can be dangerously misleading. Approximately 25–30% of patients with NIHSS ≤ 5 at presentation have a large vessel occlusion (LVO), and a subset of these patients will deteriorate significantly within hours. The phenomenon of “early neurological deterioration” (END) occurs in approximately 15–30% of patients initially categorised as mild stroke.
Clinical impact: The term “minor stroke” should not create complacency. A patient with NIHSS 3 from isolated hand weakness due to proximal MCA occlusion is at high risk of catastrophic deterioration if the clot propagates. All patients with acute ischaemic stroke — regardless of NIHSS score — should receive vascular imaging (CTA at minimum) to assess for LVO. Treatment decisions should consider the NIHSS alongside imaging findings, not the NIHSS in isolation.
Items 5 and 6 (motor arm and leg) are the most commonly miscored NIHSS items. The distinction between score 1 (drift — limb drifts but does not contact the bed before the full time period) and score 2 (some effort against gravity — limb falls to the bed before the time period ends) carries significant clinical implications, as a change from 1 to 2 represents meaningful motor worsening.
Solution: Count seconds aloud and use the full 10-second (arms) or 5-second (legs) observation period. The key distinction is: at score 1, the limb is still in the air when time expires (though lower than where it started); at score 2, the limb has contacted the bed before time is up. Document the position (e.g., “right arm drifted to 20° at 10 seconds” vs “right arm fell to bed at 4 seconds”) to improve serial comparison.
The NIHSS was developed as a research measurement tool for clinical trials — it was not designed to be a standalone treatment decision instrument. Major treatment trials (NINDS, ECASS-III, MR CLEAN, DAWN, DEFUSE-3) used the NIHSS as one component of eligibility criteria alongside imaging findings, time from onset, patient age, comorbidities, and other factors. Using NIHSS thresholds as rigid inclusion/exclusion criteria for treatment is an oversimplification of the evidence.
Clinical impact: A patient with NIHSS 3 and a confirmed ICA occlusion on CTA is not “too mild for treatment” — they are at imminent risk of devastating stroke progression. Conversely, a patient with NIHSS 25 may have a very high risk of haemorrhagic transformation with thrombolysis (approximately 6–8% symptomatic ICH rate at NIHSS > 20). Treatment decisions require a synthesis of NIHSS, imaging, timing, and patient-specific factors — the NIHSS is one input, not the decision itself.
The NIHSS does not assess dysphagia, urinary function, cognitive domains beyond language and attention, emotional state, or functional independence. A patient may have an NIHSS of 0 yet have significant cognitive impairment, dysphagia risk, or functional disability from their stroke. Always perform a comprehensive neurological examination beyond the NIHSS, including a swallow screen before oral intake.
Quick Reference Summary
| Item | Domain | Max Score | Key Assessment |
|---|---|---|---|
| 1a | LOC — Responsiveness | 3 | Observation, then stimulation |
| 1b | LOC — Questions | 2 | Month and age (first answer only) |
| 1c | LOC — Commands | 2 | Open/close eyes, grip/release |
| 2 | Best Gaze | 2 | Horizontal gaze only |
| 3 | Visual Fields | 3 | Confrontation; all four quadrants |
| 4 | Facial Palsy | 3 | Show teeth, raise brows, close eyes |
| 5a/5b | Motor — Arms (L/R) | 4 each | 90° sitting / 45° supine; 10 seconds |
| 6a/6b | Motor — Legs (L/R) | 4 each | 30° supine; 5 seconds |
| 7 | Limb Ataxia | 2 | Finger-nose, heel-shin |
| 8 | Sensory | 2 | Pin-prick; face, arms, trunk, legs |
| 9 | Best Language | 3 | Naming, reading, describing, comprehension |
| 10 | Dysarthria | 2 | Read/repeat words; speech clarity |
| 11 | Extinction/Inattention | 2 | Bilateral simultaneous stimulation |
The Golden Rule: The NIHSS score is one data point in a complex treatment decision — never the decision itself. A low NIHSS does not exclude LVO, and a high NIHSS does not automatically mandate or contraindicate treatment. Always integrate the NIHSS with vascular imaging, perfusion data, symptom onset time, and the patient’s clinical trajectory.
Disclaimer & References
For Educational Purposes Only. This calculator and the accompanying clinical information are intended as educational tools for healthcare professionals. They do not replace clinical judgement. Results should be interpreted in the full clinical context. Lab reference ranges vary by institution — verify with your own laboratory. Drug dosages should be confirmed against current prescribing information.
References
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- Lyden P, Brott T, Tilley B, et al. Improved reliability of the NIH Stroke Scale using video training. Stroke. 1994;25(11):2220-2226. DOI: 10.1161/01.STR.25.11.2220
- National Institute of Neurological Disorders and Stroke rt-PA Stroke Study Group. Tissue plasminogen activator for acute ischemic stroke. N Engl J Med. 1995;333(24):1581-1587. DOI: 10.1056/NEJM199512143332401
- Hacke W, Kaste M, Bluhmki E, et al. Thrombolysis with alteplase 3 to 4.5 hours after acute ischemic stroke (ECASS III). N Engl J Med. 2008;359(13):1317-1329. DOI: 10.1056/NEJMoa0804656
- Berkhemer OA, Fransen PS, Beumer D, et al. A randomized trial of intraarterial treatment for acute ischemic stroke (MR CLEAN). N Engl J Med. 2015;372(1):11-20. DOI: 10.1056/NEJMoa1411587
- Nogueira RG, Jadhav AP, Haussen DC, et al. Thrombectomy 6 to 24 hours after stroke with a mismatch between deficit and infarct (DAWN). N Engl J Med. 2018;378(1):11-21. DOI: 10.1056/NEJMoa1706442
- Albers GW, Marks MP, Kemp S, et al. Thrombectomy for stroke at 6 to 16 hours with selection by perfusion imaging (DEFUSE 3). N Engl J Med. 2018;378(8):708-718. DOI: 10.1056/NEJMoa1713973
- Saver JL, Altman H. Relationship between neurologic deficit severity and final functional outcome shifts over time. Stroke. 2012;43(6):1537-1541. DOI: 10.1161/STROKEAHA.111.636928
- Powers WJ, Rabinstein AA, Ackerson T, et al. Guidelines for the early management of patients with acute ischemic stroke: 2019 update (AHA/ASA). Stroke. 2019;50(12):e344-e418. DOI: 10.1161/STR.0000000000000211
- Woo D, Broderick JP, Kothari RU, et al. Does the National Institutes of Health Stroke Scale favor left hemisphere strokes? Stroke. 1999;30(11):2355-2359. DOI: 10.1161/01.STR.30.11.2355