Medicare Beneficiary Identifier (MBI)
The Medicare Beneficiary Identifier (MBI) is the unique, randomly generated 11-character alphanumeric code on a person's Medicare card that identifies them in Medicare claims and related transactions, replacing the older Social Security number-based identifier.
Updated
The Medicare Beneficiary Identifier (MBI) is the unique identifier that appears on a person's Medicare card and identifies that individual in Medicare transactions such as claims, eligibility checks, and claim status inquiries. It is an 11-character, alphanumeric value that is randomly generated so that it carries no embedded meaning and is not derived from the beneficiary's Social Security number or other personal data.
CMS introduced the MBI to replace the older Social Security number-based identifier that previously appeared on Medicare cards, as part of a broader effort to reduce the exposure of Social Security numbers and the risk of identity theft. New Medicare cards displaying the MBI were mailed to people with Medicare, and the MBI became the identifier used on Medicare fee-for-service billing and related transactions. The exact format conventions and any handling rules are defined by CMS, so its published guidance is the controlling reference.
In practice
In billing workflows, the MBI is the beneficiary identifier used when submitting Medicare fee-for-service claims and when checking a patient's Medicare eligibility or the status of a submitted claim. Because the MBI is randomly generated and unrelated to the Social Security number, staff generally capture it from the patient's current Medicare card or through the eligibility systems that CMS makes available to providers and their billing agents.
Operational details, valid character conventions, and any transition or handling requirements are set by CMS and can change over time, so authoritative CMS guidance (including Medicare Learning Network materials and the Internet-Only Manuals) is the appropriate source rather than any fixed figure or universal rule. Practices that vary by contractor, system, or program should be confirmed against that guidance rather than assumed.
Commonly confused with
- Health Insurance Claim Number (HICN): The HICN was the older Medicare identifier that was based on a beneficiary's Social Security number. The MBI replaced it specifically to remove the Social Security number from the Medicare card; the two identify the same beneficiary but are structured differently.
- Medicare Advantage (Part C) plan member ID: A person enrolled in a Medicare Advantage plan also receives a member ID issued by that private plan for use in plan transactions. That plan ID is separate from the MBI, which is the identifier assigned by Medicare itself.
- National Provider Identifier (NPI): The NPI identifies a health care provider or organization, not a patient. The MBI identifies the Medicare beneficiary. Both may appear on a claim but they serve entirely different roles.