Common Questions

Medicare Letters and Their Meaning

Learn about the meaning of the letters on your Medicare card, and explore the parts of Medicare and what their letter names mean.

What do the Medicare letters mean?

The four different parts of Medicare are each identified by a letter: A, B, C and D. The number displayed on your Medicare card, however, is known as the Medicare Beneficiary Identifier and is randomly generated for you.

What is the meaning of these Medicare letters? Here we break them down so that you can have a clearer understanding of your Medicare coverage.

What do the letters on your Medicare card mean?

The Medicare number displayed on your red, white and blue Medicare card (known as an MBI, or Medicare Beneficiary Identifier) is 11 characters long:

  • The 2nd, 5th, 8th and 9th characters are always a letter, and the 3rd and 6th characters are sometimes a letter.
  • All other characters will be numbers, and the letters S, L, O, I, B and Z will never be used.

The MBI is randomly generated and is “non-intelligent,” which means it contains no hidden or special meaning and is therefore more difficult for someone to use to steal your identity or commit fraud.

What the letters mean for the parts of Medicare

The four different parts of Medicare are each identified by a letter.

  • Medicare Part A is hospital insurance and provides coverage for inpatient stays at hospitals and skilled nursing care facilities, among other inpatient services.

  • Medicare Part B is medical insurance and provides coverage for outpatient doctor’s appointments and medical devices.

  • Medicare Part C, also known as Medicare Advantage, provides coverage for everything found in Part A and Part B through one plan provided by a private insurer.

    Many Medicare Advantage plans may also cover additional benefits not covered by Part A and Part B, such as prescription drugs, dental, vision, hearing, wellness programs like SilverSneakers and more.

  • Medicare Part D provides coverage exclusively for prescription drugs.

    You can visit to compare Part D plans available where you live and enroll in a Medicare prescription drug plan online in as little as 10 minutes.1

Medicare Supplement Insurance, also called Medigap, uses a letter system to identify its plans. Medicare Supplement Insurance is used in conjunction with Part A and Part B of Medicare to provide coverage for certain out-of-pocket expenses like some Medicare deductibles and coinsurance.

There are 10 Medicare Supplement Plans to choose from, identified by letters: Plan A, B, C, D, F, G, K, L, M and N. Note that Medigap coverage options are referred to as “plan” (e.g., Medigap Plan A) as opposed to “part” (Medicare Part A hospital insurance).

Call a licensed insurance agent

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About the author

Christian Worstell is a licensed insurance agent and a Senior Staff Writer for He is passionate about helping people navigate the complexities of Medicare and understand their coverage options.

His work has been featured in outlets such as Vox, MSN, and The Washington Post, and he is a frequent contributor to health care and finance blogs.

Christian is a graduate of Shippensburg University with a bachelor’s degree in journalism. He currently lives in Raleigh, NC.

Where you've seen coverage of Christian's research and reports:

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