The Centers for Medicare and Medicaid Services (CMS) uses information from member satisfaction surveys, plans, and health care providers to give overall performance or "Star Ratings" to Medicare Part D prescription drug plans and Medicare Advantage plans.

A Medicare plan can receive a rating from one to five stars. A 5-star rating is considered excellent. The overall plan's Star Rating gives you a single summary score that makes it easier to compare plans based on quality and performance.  A consistently low-rated Medicare plan can lose its contract with CMS.

Medicare Health Plans (Medicare Advantage)

For Medicare Advantage plans (MAs) covering health services (Medicare Part A and Medicare Part B), the overall score for quality of those services covers 42 different topics in five categories:

• Staying Healthy: Screenings, Tests and Vaccines
  Includes how often members got various screening tests, vaccines, and other check-ups that help them stay healthy.
   
• Managing Chronic (Long Term) Conditions
  Includes how often members with different conditions got certain tests and treatments that help them manage their condition.
   
• Member Experience with Health Plan
  Includes ratings of member satisfaction with the plan.
   
• Member Complaints and Changes in the Health Plan’s Performance
  Includes how often members filed a complaint against the plan.
   
• Health Plan Customer Service
  Includes how well the plan handles calls from members.

Medicare Part D Prescription Drug Plans (stand-alone PDPs)

For plans covering drug services, the overall score for quality of those services covers 17 different topics in four categories:

• Drug Plan Customer Service
  Includes how well the drug plan handles calls and makes decisions about member appeals.
   
• Member Complaints and Changes in the Drug Plan’s Performance
  Includes how often members filed a complaint about the drug plan and findings from Medicare’s audit of the plan.
   
• Member Experience with the Drug Plan
  Includes member satisfaction information.
   
• Drug Safety and Accuracy of Drug Pricing
  Includes how well the drug plan prices prescriptions and provides updated information on the Medicare website. Includes information on how often members with certain medical conditions get prescription drugs that are considered safer and clinically recommended for their condition.

For more information, please see our section: "Understanding the Medicare Star Quality Ratings"

You can also read more details on the Medicare Part D plan ratings in our articles:  The Medicare Part D Plan Rating System.

Medicare Health Plans (Medicare Advantage plans with prescription drug coverage)
For Medicare Advantage plans covering both health and drug services (MAPDs), the overall score for quality of those services covers all of the topics listed above.

(Source: CMS 5-Star Plan Rating Overview)

Read more about the 5-star Special Enrollment Period