NIH Stroke Scale (NIHSS) Calculator

The NIHSS evaluates 11 neurological domains — grouped into 15 scored items — covering consciousness, gaze, vision, facial movement, motor strength in all four limbs, coordination, sensation, language, speech articulation, and attention. Each item is scored on an ordinal scale, typically 0 (normal) to 2, 3, or 4 (most impaired), with untestable items scored by the examiner using clinical judgment. The total score is the simple arithmetic sum of all item scores and ranges from 0 to 42.

Severity is stratified as follows: a score of 0 indicates no stroke symptoms; 1–4 = minor stroke; 5–15 = moderate stroke; 16–20 = moderate-to-severe stroke; and 21–42 = severe stroke. For IV alteplase (tPA) consideration in ischemic stroke, most guidelines target an NIHSS of 4–25, though clinical context always governs the final decision. The scale is designed to be administered in approximately 6–8 minutes by a trained clinician, and certification training is freely available through the NINDS.

Beyond the emergency setting, the NIHSS is used to monitor neurological deterioration or improvement over time, stratify patients for endovascular thrombectomy candidacy, predict functional outcomes at discharge, and serve as a primary endpoint in stroke clinical trials. Higher NIHSS scores are associated with larger infarct volumes on imaging, greater disability at 90 days, and increased mortality.

The NIHSS has several important limitations clinicians should recognize. First, it is heavily weighted toward anterior (left hemisphere) strokes — posterior circulation strokes affecting the brainstem or cerebellum may score deceptively low despite causing life-threatening deficits such as impaired swallowing, gaze palsy, or rapidly progressive cerebellar herniation. Second, the scale requires trained administration; interrater reliability, while generally good (weighted kappa 0.69–0.88), decreases significantly without standardized certification. Third, the NIHSS does not capture all clinically important deficits — executive dysfunction, memory impairment, and neuropsychiatric symptoms are absent from the scale. Fourth, patients with pre-existing neurological deficits (e.g., prior stroke, dementia) may score higher at baseline, complicating interpretation of acute change. Finally, the NIHSS is a severity quantifier, not a diagnostic tool — it must always be interpreted alongside neuroimaging, clinical history, and time of symptom onset for appropriate treatment decisions.