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Medicare ID Validator

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Validate a US Medicare Beneficiary Identifier (MBI) format instantly. Checks the 11-character alphanumeric structure per CMS specifications. Free, client-side.

What is a Medicare ID?

A Medicare ID validator checks whether a given Medicare Beneficiary Identifier (MBI) follows the 11-character format defined by the US Centers for Medicare & Medicaid Services (CMS). The MBI is the identification number on every US Medicare card and is used in all healthcare billing, insurance claims, and eligibility verification transactions involving Medicare.

The MBI replaced the previous Health Insurance Claim Number (HICN) — which was derived from the beneficiary's Social Security Number — between 2018 and 2019 as part of a CMS initiative to reduce identity theft and protect beneficiary privacy. Unlike the HICN, the MBI is a randomly generated 11-character code with no relationship to any personal identifier.

The MBI follows a precise alphanumeric pattern: specific positions must be digits, others must be letters from a restricted 19-letter alphabet (excluding S, L, O, I, B, and Z to avoid visual ambiguity), and some positions may be either. The validator checks all 11 positions against these CMS rules, flagging any position that does not conform.

This is a format check only. It confirms the structural correctness of the identifier — the same check a CMS billing system performs before accepting a claim. It does not query the CMS beneficiary database and cannot confirm whether the MBI belongs to an active beneficiary. Use it alongside the NPI Validator and the EIN Validator when building healthcare billing validation workflows.

How to use this Medicare ID calculator

  1. Enter or paste the MBI into the Medicare ID (MBI) field. You can include or omit the hyphens.
  2. The result shows immediately: Valid with the formatted ID, or Invalid with a list of which positions failed and why.
  3. Correct any flagged positions and re-validate.
  4. For billing purposes, always confirm the MBI against the beneficiary's physical Medicare card.

Formula & Methodology

The 11-character MBI follows this positional pattern (C = required letter, N = required digit, A = letter or digit):

| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Rule | Digit 1–9 | Letter* | Letter* or digit | Digit | Letter* | Letter* or digit | Digit | Letter* | Letter* | Digit | Digit |

*Allowed letters: A, C, D, E, F, G, H, J, K, M, N, P, Q, R, T, V, W, X, Y (19 letters; excludes S, L, O, I, B, Z).

Valid example: 1EG4TE5MK72Invalid examples:
- 0EG4TE5MK72 — position 1 is 0 (must be 1–9)
- 1OG4TE5MK72 — position 2 is O (forbidden letter)
- 1EG4TE5MK7 — only 10 characters (must be exactly 11)

Frequently Asked Questions

A Medicare Beneficiary Identifier (MBI) is the 11-character alphanumeric ID used to identify Medicare beneficiaries in the United States. It replaced the Social Security Number-based Health Insurance Claim Number (HICN) in 2019 as part of a CMS initiative to protect beneficiary privacy. Every Medicare recipient has a unique MBI on their Medicare card.
An MBI is exactly 11 characters in a specific C A AN A AN A A NN pattern: position 1 is a digit 1–9; positions 2, 5, 8, and 9 are letters from a restricted alphabet (A–Z excluding S, L, O, I, B, Z); position 3 is either a letter or digit; position 4 is a digit; position 6 is either a letter or digit; position 7 is a digit; and positions 10 and 11 are digits.
The letters S, L, O, I, B, and Z are excluded from alphabetic positions in an MBI. S and L are excluded because they resemble digits 5 and 1. O and I are excluded because they resemble 0 and 1. B and Z are excluded as an additional safeguard against misreading. The allowed letters are A, C, D, E, F, G, H, J, K, M, N, P, Q, R, T, V, W, X, and Y.
The HICN (Health Insurance Claim Number) was the previous Medicare ID format and was based on the beneficiary's Social Security Number, making it a privacy risk. The MBI replaced it in April 2018–December 2019. MBIs are randomly generated and contain no derivable personal information, making them safer for use in healthcare transactions.
No. This tool validates only the format — that the 11 characters follow the CMS-defined pattern. It cannot confirm that the MBI is active, assigned to a living beneficiary, or not fraudulently generated. Confirming MBI authenticity requires access to the CMS beneficiary database.
The MBI appears on the front of the Medicare card, typically labelled 'Medicare Number' or 'Member ID'. It is printed in the format XXXX-XXX-XXXX (with hyphens separating characters 1–4, 5–7, and 8–11). The validator accepts the ID with or without hyphens.
No. All validation happens locally in your browser. Your Medicare ID is never transmitted to a server or stored. This is important — the MBI is sensitive health information and should not be shared with untrusted third parties.
Healthcare providers, billing companies, and EHR (Electronic Health Record) systems submit claims to CMS using MBIs. A malformed MBI — one that fails the format check — will be rejected by the CMS system. Validating the format before submission catches transcription errors, preventing claim rejections and reimbursement delays.
No. This validator checks the current MBI format only. HICNs have a different structure (SSN-based, with letter suffixes). If you are working with pre-2019 Medicare identifiers, you will need to verify they have been converted to the new MBI format.
The standard display format for an MBI is four characters, hyphen, three characters, hyphen, four characters — for example, 1EG4-TE5-MK72. The hyphens are for readability only and are not part of the 11-character identifier itself.
The Centers for Medicare & Medicaid Services (CMS) issues MBIs. They are randomly generated and assigned when a beneficiary enrolls in Medicare. The MBI has no derivable relationship to the beneficiary's personal information — it is a random identifier.
Also known as
Medicare ID checkMBI validatorMedicare Beneficiary Identifiervalidate Medicare numberCMS MBI