The NIH Stroke Scale is the most widely used clinical instrument for quantifying the severity of an acute stroke. It converts a structured 15-item neurological examination into a single 0-42 point score that supports triage, treatment discussions, and tracking of a patient's course. This page explains how the scale is scored, how to read the total, and — critically — its limits as a self-scored calculator.
How the NIHSS works
The NIHSS sums 15 items that each probe a specific neurological function: level of consciousness (three sub-items), horizontal gaze, visual fields, facial palsy, motor strength in each arm and leg, limb ataxia, sensation, language, dysarthria, and extinction/inattention. Each item is scored on its own tiered scale — most on 0-2, several on 0-3, and the four motor-limb items on 0-4 — and the item scores are added to a total that ranges from 0 (no measurable deficit) to 42.
The scale was derived by Brott and colleagues (Stroke, 1989) and standardized through NINDS training so that different examiners produce consistent scores. Two items carry an 'untestable' (UN) option — the motor limbs for amputation or joint fusion, and dysarthria for an intubated patient — and by convention these contribute 0 points rather than a maximum.
Reading the severity tiers
A commonly used stratification maps the total to five tiers: 0 = no stroke symptoms, 1-4 = minor stroke, 5-15 = moderate stroke, 16-20 = moderate-to-severe stroke, and 21-42 = severe stroke. Higher scores correlate with larger infarcts, worse functional outcomes, and a higher symptomatic-hemorrhage risk after thrombolysis. The baseline NIHSS is also used to track change over time — a rising score during monitoring can signal extension or hemorrhagic transformation.
Importantly, the NIHSS informs but does not decide reperfusion therapy. Decisions about intravenous thrombolysis (tPA) or endovascular thrombectomy weigh the NIHSS alongside time from onset, imaging (including large-vessel occlusion and salvageable tissue), and the full list of contraindications.
Limits and how it should be used
This calculator sums the item scores you enter; it does not perform the neurological examination. A valid NIHSS depends on the exam being administered correctly by a clinician who has completed certified NIHSS training — uncertified or inconsistent scoring is a well-documented source of error. The scale also has known blind spots: it under-weights posterior-circulation and right-hemisphere strokes, so a low total does not exclude a disabling stroke.
Use this tool for education, documentation support, and communication — never as a stand-alone basis for diagnosis or treatment. Acute stroke care is time-critical and should always run through the treating stroke team and local protocols.