Quick Answer
A Medicare Beneficiary Identifier (MBI) is an 11-character alphanumeric code that serves as your unique Medicare ID. It replaced Social Security Number-based Health Insurance Claim Numbers (HICNs) on all Medicare cards in 2019 to protect against identity theft.
Coverage Comparison by Plan Type
| Plan Type | Coverage | Notes |
|---|---|---|
| Medicare Beneficiary Identifier (MBI) | Current Medicare ID — used for all Medicare transactions since 2019 | 11-character alphanumeric; no SSN embedded |
| Health Insurance Claim Number (HICN) | Old Medicare ID — based on Social Security Number | No longer accepted; replaced by MBI in 2019 |
| Medicare Card | Red, white, and blue card showing your MBI and coverage dates | Keep in a safe place; carry a copy when seeking care |
| Medicare Advantage ID Card | Issued by your MA plan; use this card (not red/white/blue) for care | Your MBI is still on file but you use your plan's card |
Understanding Your Coverage Options
What is an MBI?
The Medicare Beneficiary Identifier (MBI) is a randomly generated 11-character code consisting of numbers and uppercase letters. It is unique to each Medicare beneficiary and is used for all Medicare billing and transactions.
CMS replaced the old SSN-based Health Insurance Claim Number (HICN) with the MBI starting in April 2018. By December 2019, all Medicare cards had been replaced with new cards featuring the MBI.
What It Covers
- Used for all Medicare Part A and Part B billing
- Required for Medicare Advantage and Part D transactions
- Used when filing Medicare claims
- Needed when enrolling in Medicare or changing plans
What It Doesn't Cover
- MBI is not the same as your Medicare Advantage plan ID
- MBI does not contain any personal information (it's randomly generated)
- MBI is not used for Social Security transactions
MBI Format Explained
The MBI follows a specific 11-character format: 1C2AC2AC2AC3. Each position uses either a number (0-9) or an uppercase letter (A-Z), but the letters S, L, O, I, B, and Z are never used to avoid confusion with numbers.
The MBI is case-sensitive and must be entered exactly as shown on your Medicare card. There are no dashes or spaces in the MBI itself, though it may be displayed with dashes for readability.
What It Covers
- Position 1: Always a number (1-9)
- Positions 2, 5, 8: Always an uppercase letter (not S, L, O, I, B, Z)
- Positions 3, 6, 9: Always a number or letter
- Positions 4, 7, 10, 11: Always a number
What It Doesn't Cover
- Letters S, L, O, I, B, Z are never used
- The number 0 is used but the letter O is not
- MBIs are randomly generated and carry no personal meaning
Example MBI Format
An MBI looks like: 1EG4-TE5-MK72. The dashes are for display only. When entering your MBI for billing, use all 11 characters without dashes.
How to Find Your MBI
Your MBI is printed on your red, white, and blue Medicare card. If you've misplaced your card, there are several other ways to find your MBI.
What It Covers
- Medicare card: Your MBI is printed on the front
- Medicare.gov account: Log in and view your MBI online
- Medicare Summary Notice (MSN): Your MBI appears on your MSN
- Call 1-800-MEDICARE (1-800-633-4227) to get your MBI
What It Doesn't Cover
- Social Security cannot provide your MBI (contact Medicare directly)
- Your doctor's office may have it on file from previous visits
Protect Your MBI
Treat your MBI like your Social Security Number. Never share it with anyone who contacts you unsolicited. Medicare will never call you to ask for your MBI.
Lost or Stolen Medicare Card
If your Medicare card is lost, stolen, or damaged, you can get a replacement card for free. Your MBI will remain the same unless you report fraud.
What It Covers
- Request online at Medicare.gov (fastest method)
- Call 1-800-MEDICARE to request a replacement
- Visit your local Social Security office
- Replacement cards arrive by mail within 30 days
What It Doesn't Cover
- You cannot get a replacement card at a Medicare office (there are none)
- If fraud occurred, report it and request a new MBI
Medicare Card & MBI Quick Reference
| Item | Details | Where to Find |
|---|---|---|
| Medicare Beneficiary Identifier (MBI) | 11-character alphanumeric ID | Medicare card, Medicare.gov, MSN |
| Medicare Card | Red, white, and blue card | Mailed when you enroll; replace at Medicare.gov |
| Medicare Advantage Card | Issued by your MA plan | Mailed by your plan after enrollment |
| Part D Card | Issued by your drug plan | Mailed by your Part D plan after enrollment |
| Medicare Summary Notice | Quarterly statement of claims | Mailed quarterly or view at Medicare.gov |
✦ Important Exceptions & Special Situations
Medicare Advantage Members
If you have Medicare Advantage, you use your plan's ID card (not your red/white/blue Medicare card) when seeking care. However, your MBI is still on file and may be needed for certain transactions.
Reporting Medicare Fraud
If you believe someone has used your MBI fraudulently, report it to 1-800-MEDICARE or the Office of Inspector General at 1-800-HHS-TIPS. You can request a new MBI if your identity has been compromised.
Never share your MBI with anyone who contacts you unsolicited.
Railroad Retirement Board (RRB) Beneficiaries
If your Medicare coverage is through the Railroad Retirement Board, your Medicare card and ID number may look different. Contact the RRB at 1-877-772-5772 for assistance.
Providers Still Using Old HICN
Since the 2019 transition, all Medicare transactions must use the MBI. If a provider is still using your old HICN, remind them to update their records with your MBI to avoid claim rejections.
✦ Background: The MACRA MBI Transition
Medicare Access and CHIP Reauthorization Act (MACRA) U2014 MBI Mandate
PassedMACRA (2015) required CMS to remove Social Security Numbers from Medicare cards and replace them with new Medicare Beneficiary Identifiers by April 2019. The transition was completed by December 2019.
New Medicare Card Mailing Completed
PassedCMS mailed new Medicare cards to all 58 million beneficiaries between April 2018 and December 2019. The transition was completed on schedule, protecting beneficiaries from SSN-based identity theft.
Protecting Your Medicare Card & MBI
Your MBI is sensitive personal information. Follow these steps to protect it and respond quickly if it's compromised.
Security Checklist
- Keep your Medicare card in a safe place — don't carry it unless needed
- Never share your MBI with unsolicited callers, even if they claim to be from Medicare
- Review your Medicare Summary Notice (MSN) for unfamiliar claims
- Create a Medicare.gov account to monitor your claims online
- Report suspected fraud to 1-800-MEDICARE or 1-800-HHS-TIPS
- If your card is lost or stolen, request a replacement at Medicare.gov immediately
✦ Frequently Asked Questions
David Haass
AuthorDavid Haass is a licensed insurance agent and Medicare specialist at MedicareFAQ.com.
Ashlee Zareczny
ReviewerAshlee Zareczny is the Compliance & Editorial Manager at MedicareFAQ.