A 1-to-5 star summary CMS calculates by combining measures from five categories: mortality, safety of care, readmission, patient experience, and timely and effective care.
Why this matters to you
It is a starting point, not a verdict. The rating averages performance across many conditions, so a hospital can be excellent at cardiac surgery and average overall. If you know what care you need, the individual measure matters more. And roughly two in five hospitals have no star rating at all, which is usually about low patient volumes rather than poor care.
Official source
The authoritative definition and current rules are published here:
Rules and figures change. Where this page and the official source disagree, the official source is correct — and we would like to know, so please tell us.