Understanding the Medicare Beneficiary Identifier (MBI)

What is the Medicare Beneficiary Identifier?

The Medicare Beneficiary Identifier (MBI) is a unique identifier assigned to each person with Medicare. This randomly generated series of numbers and letters replaces the Social Security Number-based Health Insurance Claim Number (HICN) previously used to identify Medicare beneficiaries.

The MBI serves as the official Medicare card identifier that healthcare providers, insurance companies, and Medicare beneficiaries use when submitting claims, verifying coverage, and otherwise interacting with the Medicare program. The transition to the MBI was implemented as part of the Social Security Number Removal Initiative (SSNRI) to help protect Medicare beneficiaries from identity theft and fraud.

Transition from Social Security Numbers

Prior to April 2018, Medicare cards displayed Social Security Numbers (SSNs) as the primary identifier. This posed significant security risks, as SSNs are valuable pieces of personal information often used by identity thieves. The Medicare Access and CHIP Reauthorization Act of 2015 mandated that CMS (Centers for Medicare & Medicaid Services) remove SSNs from all Medicare cards.

The transition period ran from April 2018 to April 2019, during which new Medicare cards with MBIs were mailed to all Medicare beneficiaries. This major change affected approximately 60 million Americans receiving Medicare benefits.

MBI Format and Structure

The MBI consists of 11 characters that are randomly generated and include both numbers and uppercase letters. Each character has specific rules:

Characters 1-4: Can be any number 0-9 or any letter except S, L, O, I, B, or Z
Character 5: Can be any number 0-9 or any letter except S, L, O, I, B, or Z
Character 6: Always a number 0-9
Character 7: Can be any number 0-9 or any letter except S, L, O, I, B, or Z
Character 8: Can be any number 0-9 or any letter except S, L, O, I, B, or Z
Character 9: Can be any number 0-9 or any letter except S, L, O, I, B, or Z
Character 10: Always a number 0-9
Character 11: Can be any number 0-9 or any letter except S, L, O, I, B, or Z

For display purposes, the MBI is formatted with hyphens in specific positions (4-5-2) to improve readability. However, for electronic claims processing, the hyphens should be removed.

The letters S, L, O, I, B, and Z are intentionally excluded from MBIs to prevent confusion with similar-looking numbers.

Components of the MBI

Position	Possible Values	Purpose
Position 1-4	0-9, A-Z (except S, L, O, I, B, Z)	Identifies the beneficiary
Position 5	0-9, A-Z (except S, L, O, I, B, Z)	Sequencing identifier
Position 6	0-9 only	Serves as a separator
Position 7-9	0-9, A-Z (except S, L, O, I, B, Z)	Identifies the beneficiary
Position 10	0-9 only	Serves as a separator
Position 11	0-9, A-Z (except S, L, O, I, B, Z)	Checksum digit

Using Your MBI

Your MBI appears on your Medicare card and serves as your primary identifier when interacting with the healthcare system. You'll need to provide your MBI when:

• Visiting healthcare providers who treat Medicare patients
• Filing Medicare claims
• Contacting Medicare representatives
• Enrolling in Medicare Advantage plans or Part D prescription drug plans
• Interacting with insurance companies that coordinate benefits with Medicare

Replacing a Lost MBI Card

If your Medicare card is lost or damaged, you can request a replacement through several methods:

1. By logging into your secure Medicare account at Medicare.gov
2. By calling 1-800-MEDICARE (1-800-633-4227)
3. By visiting your local Social Security office
4. If you have Medicare through a Medicare Advantage plan, you may contact your plan directly

Replacement cards typically arrive within 30 days of your request. In emergency situations, healthcare providers can verify your Medicare coverage using other information if you don't have your card available.

Protecting Your MBI from Fraud

While the MBI provides better security than the previous Social Security Number-based identifiers, it's still important to protect yourself from Medicare fraud:

• Never share your MBI with anyone who contacts you unsolicited
• Beware of callers claiming to represent Medicare who ask for payment or personal information
• Guard your Medicare card carefully and report it immediately if lost or stolen
• Review your Medicare Summary Notices regularly for suspicious activity
• Report suspected Medicare fraud by calling 1-800-MEDICARE

MBI and Electronic Claims Processing

Healthcare providers and billing entities must update their systems to accommodate the MBI for claims processing. Electronic claims require the MBI to be entered without hyphens, while paper claims should reflect the hyphenated format.

Healthcare providers were given an eight-month transition period to implement the necessary changes to their billing systems, beginning with CMS issuing 100 percent MBI-only claims in October 2019.

Questions About Your MBI

Will my MBI ever change?

Yes, there are circumstances in which your MBI might change. If you return to Medicare after disenrolling, if your Medicare entitlement changes, or if the original MBI was compromised due to identity theft, you will receive a new MBI.

How do I tell my doctors about my new MBI?

When you visit your healthcare providers, show them your new Medicare card so they can update their records with your MBI. This ensures your claims will be processed correctly.

What if someone still has my old HICN?

Your HICN will no longer be accepted for Medicare claims after the transition period. If someone still has your old identifier, they cannot use it to bill Medicare for services.

Does my MBI replace my Social Security Number for all purposes?

No. Your MBI is used exclusively for Medicare-related transactions. Your Social Security Number remains your official identifier for other government programs and purposes.

Resources for More Information

To learn more about the Medicare Beneficiary Identifier or Medicare in general, visit Medicare.gov or call 1-800-MEDICARE (1-800-633-4227). TTY users can call 1-877-486-2048. Medicare representatives are available 24 hours a day, 7 days a week.