How often are CMS star ratings updated?

CMS refreshes the Overall Hospital Quality Star Rating periodically, generally once a year. The underlying data covers earlier time periods, so a rating reflects past performance.

Is a 5-star hospital always better than a 3-star hospital?

Not for every patient or every condition. The rating is a summary of many measures. A 3-star hospital may perform better on the specific care you need, so look at the detailed measures as well.

Why did my hospital's rating change?

Ratings change when new data comes in, when other hospitals' performance changes, or when CMS adjusts the methodology. Because stars are assigned relative to peer hospitals, a hospital's rating can move even if its own results stay similar.

Where can I see the details behind a rating?

On Medicare.gov Care Compare, search for the hospital and open its quality information. You can view each measure group and many of the individual measures.

How CMS Hospital Star Ratings Work

The Overall Hospital Quality Star Rating is a score from 1 to 5 stars that the Centers for Medicare & Medicaid Services (CMS) gives to many US hospitals. It appears on Medicare.gov Care Compare and in our directory, where you can browse 5-star hospitals and 4 and 5-star hospitals. The rating is a useful starting point, but it summarizes a lot of data into one number, so it helps to know what goes into it and what it leaves out.

What the star rating measures

CMS builds the overall rating from quality measures that hospitals already report publicly on Care Compare. Those measures are sorted into five measure groups:

Measure group	What it looks at	Weight in the overall score
Mortality	Death rates within 30 days for conditions such as heart attack, heart failure, pneumonia, stroke and after certain surgeries	22%
Safety of care	Healthcare-associated infections, complications after hip and knee replacement, and other patient safety indicators	22%
Readmission	How often patients return to the hospital unexpectedly after discharge, including returns to the emergency department	22%
Patient experience	Results of the HCAHPS patient survey about communication, responsiveness, cleanliness and more	22%
Timely and effective care	Process measures such as emergency department timing and use of recommended treatments	12%

The patient experience group comes from the HCAHPS survey, which is explained in What Is the HCAHPS Patient Survey?.

How the stars are calculated

In simplified terms, the method works like this:

Each measure is standardized so measures with different scales can be compared.
Measure group scores are calculated as the average of the standardized measures in that group.
A summary score is calculated by weighting the five group scores as shown above. If a hospital has no measures in a group, the weights of the remaining groups are adjusted.
Hospitals are placed into peer groups based on how many measure groups they report: three, four or five. This aims to compare similar hospitals with each other.
Stars are assigned within each peer group using a statistical clustering method, from 1 star for the lowest summary scores to 5 stars for the highest.

To receive a rating, a hospital must report at least three measures in at least three measure groups, and one of those groups must be mortality or safety of care. CMS updates the ratings periodically, generally once a year, using data that can be one to several years old depending on the measure.

Why some hospitals have no star rating

Many hospitals do not have an overall rating. Common reasons include:

Too few measures or cases: small hospitals, including many critical access hospitals, may not report enough data.
Hospital type: children's hospitals, psychiatric hospitals, long-term care hospitals and some specialty hospitals are not rated, partly because the measures are designed around adult acute care for Medicare patients.
Federal hospitals: some federal facilities are rated differently or not included, depending on what they report.

A missing rating does not mean a hospital is unsafe. It means CMS did not have enough comparable data to calculate a score.

What the stars can tell you

A star rating gives a broad view of how a hospital performs on common conditions compared with similar hospitals. Higher-rated hospitals have, on average, done better across mortality, safety, readmissions and patient experience. That is useful when you are choosing among several hospitals for planned care.

What the stars do not tell you

Performance for your specific procedure. A hospital with an average overall rating might be excellent at the one surgery you need, and the reverse can be true. Look at procedure-specific measures, volume, and surgeon experience.
Current conditions. Data lags behind. Leadership, staffing and processes may have changed since the data period.
Everything about safety. The safety group covers specific measured events, not every kind of error.
Cost or access. The rating says nothing about price, insurance networks or wait times.
Small differences. Two hospitals near the boundary between 3 and 4 stars may perform very similarly.

Using star ratings well

Compare hospitals within a similar distance and of a similar type.
Click into the measure groups on Care Compare to see where a hospital is strong or weak.
Look at the patient survey results if communication matters to you.
Combine the CMS rating with other sources, such as The Joint Commission's accreditation status, the Leapfrog Hospital Safety Grade, and state reports on infections or specific procedures.
Ask your doctor where they would send a family member for the care you need.

For a full checklist, see How to Choose a Hospital.

Other CMS ratings and designations

The overall star rating is separate from other CMS information on Care Compare, such as the HCAHPS summary star rating for patient experience and the Birthing-Friendly designation for hospitals that meet certain maternity care quality criteria. See How to Choose a Hospital to Give Birth and birthing-friendly hospitals.