Medicare Assignment of Benefits (AOB) Form: Signing, Commitments, and Revocation

There is no standalone Medicare Assignment of Benefits form with its own CMS form number. The assignment authorization is built into the CMS-1500 claim form that your provider uses to bill Medicare for Part B services, and you complete it by signing two lines on that form at your provider’s office. Your signature directs Medicare to pay the provider directly and, when the provider accepts assignment, binds them to accept the Medicare-approved amount as payment in full. You are then responsible only for the annual Part B deductible ($283 in 2026) and the standard 20 percent coinsurance.1CMS. 2026 Medicare Parts A and B Premiums and Deductibles

Where You Actually Sign

Three items on the CMS-1500 work together to create the assignment.2Centers for Medicare & Medicaid Services. CMS-1500 Health Insurance Claim Form You sign two of them; the provider marks the third.

  • Item 12 — Release of Information. Your signature authorizes the release of medical information Medicare needs to process the claim. It is a prerequisite for the assignment, not the assignment itself.3NUCC. 1500 Health Insurance Claim Form Reference Instruction Manual
  • Item 13 — Assignment of Benefits. This is the actual assignment. Your signature authorizes Medicare to send payment directly to the provider. If you also carry a Medigap policy and the required Medigap information appears elsewhere on the form, this same signature can authorize payment of Medigap benefits to the provider.4Centers for Medicare & Medicaid Services. Medicare Claims Processing Manual Chapter 26 – Completing and Processing Form CMS-1500 Data Set
  • Item 27 — Accept Assignment. The provider checks “Yes” or “No” to indicate whether they are accepting assignment on that particular claim. You do not sign this item.

Most provider offices ask you to sign Items 12 and 13 once, during intake. On every claim after that, the billing department notes “signature on file” and references the original. You do not re-sign at each visit. The signature-on-file authorization remains valid until you revoke it in writing.

What Information You Need to Provide

Your part of the form is short. The provider needs your full legal name exactly as it appears on your Medicare card and your Medicare Beneficiary Identifier (MBI), the 11-character string of numbers and uppercase letters printed on the red, white, and blue card that CMS began issuing in 2018.5Centers for Medicare & Medicaid Services. Understanding the Medicare Beneficiary Identifier (MBI) Format A name mismatch or a typo in the MBI will cause the claim to be rejected.

Everything else — the provider’s National Provider Identifier, dates of service, diagnosis codes, procedure codes — comes from the provider’s billing system. The dates of service matter to you only in one respect: the assignment applies to the encounters listed on the claim, so a signature on file does not retroactively assign benefits for services billed before you signed.

What You Commit To When You Sign

Signing Item 13 does two things. It routes Medicare’s payment to the provider instead of to you, and when combined with the provider checking “Yes” on Item 27, it holds the provider to the Medicare-approved amount. They can bill you for your deductible and coinsurance and nothing more.

Whether assignment is in play on a given claim depends on the provider’s status with Medicare:

  • Participating providers have signed a contract agreeing to accept assignment on every Medicare claim. About 96 percent of physicians fall into this category. Because assignment is built into their participation agreement, you do not need to sign anything separate — the status handles it.
  • Non-participating providers decide claim by claim. When they accept assignment, the same rules apply, but Medicare pays them at 95 percent of the full fee schedule rate. When they do not, you typically pay the full bill at the time of service and wait for Medicare to reimburse you. Federal law caps what they can charge at 115 percent of the non-participating fee schedule amount, a ceiling called the limiting charge. Either way, they must still submit the claim to Medicare for you and cannot charge a fee for doing so.6Social Security Administration. Social Security Act 1842 – Provisions Relating to the Administration of Part B7Medicare. Does Your Provider Accept Medicare as Full Payment8Noridian Healthcare Solutions. NonParticipation – JE Part B

When You Don’t Need to Sign Anything

For certain categories of services, federal law requires providers to accept assignment regardless of their participation status. In these situations, assignment is a condition of payment itself — the provider either bills on an assignment basis or does not get paid at all — and no signature from you is required to make it work.

When Signing Won’t Help: Opted-Out Providers

A small number of physicians formally opt out of Medicare. They file an affidavit with their Medicare Administrative Contractor and sign a private contract with each Medicare beneficiary before providing any services. That private contract must state that you are giving up your right to Medicare payment for those services, that Medigap plans will not cover them, and that you have the right to see an enrolled provider instead. The opt-out period lasts two years and renews automatically unless the physician cancels it.12Palmetto GBA. Private Contract Sample for Providers That Opt Out of Medicare

If you see an opted-out provider, assignment does not apply at all. There is nothing to sign on a CMS-1500 because no claim is going to Medicare. You pay the provider’s full cash rate, and neither Medicare nor your Medigap insurer will reimburse you. The one exception is emergency care, where an opted-out physician may treat a Medicare beneficiary without a private contract and bill Medicare for that encounter.

Medigap Crossover: One Signature, Two Payments

If you carry a Medigap (Medicare Supplement) policy, your signature in Item 13 can trigger an automatic handoff of claim data to your Medigap insurer so you don’t have to file a separate claim for the remaining 20 percent. This automatic transfer is called a crossover claim, and it works only when the provider is a participating Medicare provider and the correct Medigap information appears on the form.13CGS Medicare. Crossover Claims

For crossover to happen, the provider needs to include your Medigap policy number in Item 9a and the insurer’s five-digit Coordination of Benefits Agreement (COBA) ID in Item 9d. Your signature in Item 13 then authorizes both the Medicare assignment and the Medigap payment to the provider. If the COBA ID is missing, Medicare still processes its share, but your supplemental claim won’t cross over automatically and you’ll need to file it yourself.

How to Revoke the Authorization

You can cancel a signature-on-file authorization at any time by notifying your provider in writing. There is no CMS form for this. A dated letter to the provider’s billing department stating that you are revoking the assignment authorization is enough. Once revoked, the provider can no longer use your previous signature to bill Medicare on an assignment basis for future services. Revocation does not affect claims already submitted — it applies going forward.

Revoking assignment changes the payment flow, not the coverage. Medicare still covers the same services. What changes is that you may need to pay the provider directly and wait for Medicare to reimburse you, and a non-participating provider is no longer bound by the Medicare-approved amount for your claims, though the limiting charge still caps what they can bill.