Medicare Beneficiary Identifier
The MBI uses numbers and uppercase letters, omitting S, L, O, I, B, and Z. It is not a 10-digit NPI.
Source: CMS, Medicare Beneficiary Identifiers. Page read October 14, 2026.
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Definition · Medicare program and benefits
Medicare Beneficiary Identifier
A Medicare Beneficiary Identifier is the 11-character number on a Medicare card. CMS replaced the old Health Insurance Claim Number, which was based on a Social Security number. An MBI identifies the person. An NPI identifies the provider. This site does not look up MBIs and does not store them.
Questions
Medicare Beneficiary Identifier, answered
Is an MBI an NPI?
No. The MBI is the person's Medicare number. The NPI is the provider's number.