Calculate the NIH Stroke Scale score to quantify stroke severity, guide treatment decisions, and predict outcomes with all 15 examination items.
The National Institutes of Health Stroke Scale (NIHSS) is the gold-standard clinical assessment tool for quantifying the severity of acute ischemic stroke. First published in 1989 by Brott et al., the NIHSS systematically evaluates 15 items across major neurological domains — level of consciousness, motor function, sensory function, language, visual fields, gaze, ataxia, and neglect — producing a composite score from 0 to 42.
The NIHSS serves multiple critical roles in acute stroke care. It provides a common language for real-time communication between emergency physicians, neurologists, and interventionalists. It guides treatment decisions: scores of 5+ generally warrant IV alteplase (tPA) within the 4.5-hour window, while scores suggesting large vessel occlusion (typically ≥6) may qualify for mechanical thrombectomy up to 24 hours from onset. Serial NIHSS assessments detect neurological deterioration or improvement.
This calculator guides you through each of the 15 NIHSS examination items, computes subscore breakdowns, identifies lateralization patterns suggesting stroke hemisphere, and contextualizes the score against treatment windows and clinical significance thresholds.
The NIHSS is required for stroke treatment decisions, documentation, and inter-facility communication. This calculator ensures accurate scoring by guiding you through all 15 items with standardized options, while providing contextual analysis of subscores, lateralization, and treatment window eligibility. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain. Use this clarification to avoid ambiguous interpretation.
NIHSS Total = Sum of all 15 item scores. Items scored 0–4 (motor) or 0–3 (most others) or 0–2 (some). Maximum total = 42. Severity: 0 = no symptoms, 1–4 = minor, 5–15 = moderate, 16–20 = moderate-severe, 21–42 = severe.
Result: NIHSS 13 — Moderate Stroke
Right-sided weakness (arm 3, leg 3) with facial palsy, mild aphasia, and dysarthria suggests a left middle cerebral artery territory stroke. Score of 13 strongly supports IV tPA if within window, and thrombectomy evaluation for large vessel occlusion.
The NIHSS was developed through an NIH-funded project at the University of Cincinnati in the late 1980s. The original scale was refined from a larger set of neurological examination items to include only those with the highest inter-rater reliability and predictive validity. The scale was first used in clinical trials for the NINDS tPA Stroke Trial (1995), which established IV alteplase as the first FDA-approved treatment for acute ischemic stroke. Since then, the NIHSS has been used as the primary outcome measure in virtually every major stroke trial.
The advent of mechanical thrombectomy transformed the role of the NIHSS. Five landmark trials published in 2015 (MR CLEAN, ESCAPE, EXTEND-IA, SWIFT PRIME, REVASCAT) established thrombectomy as standard of care for large vessel occlusion stroke, using NIHSS as a key enrollment criterion. The 2018 DAWN and DEFUSE-3 trials extended the treatment window to 16–24 hours, using clinical-imaging mismatch criteria where the NIHSS score represents the "clinical" component. Understanding the NIHSS is now essential for triaging patients to thrombectomy-capable comprehensive stroke centers.
NIH provides a free online NIHSS certification program that can be completed in approximately 45 minutes. The training includes video demonstrations of each item scored on actual stroke patients, followed by a certification exam. Recertification is recommended annually. Many hospitals require NIHSS certification for all emergency department and stroke unit nurses, physicians, and advanced practice providers. Standardized training is the key to achieving the inter-rater reliability that makes serial NIHSS assessments clinically meaningful.
The NIHSS has known lateralization bias. It includes 7 points for language (aphasia + dysarthria) but only 2 points for neglect/extinction. Since aphasia occurs with dominant (usually left) hemisphere strokes and neglect with non-dominant (right) hemisphere strokes, left-hemisphere strokes tend to score higher. A right MCA occlusion causing severe neglect but no aphasia may score 12, while a comparable left MCA occlusion with aphasia may score 18. This is important because treatment decisions should not rely solely on NIHSS in suspected right-hemisphere stroke.
IV alteplase (tPA) is generally considered for NIHSS ≥5 within 4.5 hours of onset, though it can be given for lower scores with disabling deficits. For mechanical thrombectomy, trials (MR CLEAN, ESCAPE, EXTEND-IA, SWIFT PRIME, REVASCAT) enrolled patients with NIHSS ≥6 and confirmed large vessel occlusion (LVO). The DAWN and DEFUSE-3 trials extended the thrombectomy window to 24 hours for select patients with favorable imaging profiles (clinical-core mismatch).
The NIHSS is a strong predictor of short-term and long-term outcomes. An initial NIHSS of 16+ predicts a high probability of death or severe disability, while NIHSS ≤6 predicts a good recovery. However, posterior circulation strokes (basilar artery, cerebellar) may have low NIHSS scores despite potentially fatal outcomes, because the NIHSS tests predominantly anterior circulation functions. A normal NIHSS does not rule out posterior circulation stroke.
Yes. The NIHSS was specifically designed for administration by non-neurologists. Studies show high inter-rater reliability among trained emergency physicians, nurses, and paramedics. Video-based certification courses (freely available from the NIH) provide standardized training. Key scoring principles: score what the patient does (not what you think they can do), give the first try more weight, and don't coach the patient.
Standard stroke protocols recommend NIHSS assessment: (1) at initial presentation, (2) at 2 hours after tPA, (3) at 24 hours, (4) before any procedure (thrombectomy), (5) after any procedure, and (6) at discharge. A 4+ point increase from baseline suggests hemorrhagic conversion or re-occlusion and warrants immediate CT imaging. Serial trending is more valuable than any single score.
The NIHSS has a well-known blind spot for posterior circulation (vertebrobasilar) strokes. These strokes affect brainstem, cerebellum, and occipital lobe — causing vertigo, diplopia, ataxia, cranial nerve palsies, and bilateral motor deficits. The NIHSS has limited items for ataxia (0–2) and no items for vertigo, nystagmus, or cranial nerve deficits other than gaze and facial palsy. A basilar artery occlusion causing coma may paradoxically score lower than a mild MCA stroke with aphasia. Clinical suspicion should override a low NIHSS in suspected posterior circulation events.