Assignment of Benefits (AOB)
Assignment of benefits (AOB) is the patient's written authorization directing their insurer to pay the provider directly instead of sending payment to the patient. It is captured at registration, indicated in box 13 of the CMS-1500 and the 837 file, and without it payers can mail the check to the patient.
- Purpose
- Payer pays the provider, not the patient
- Captured
- At registration, in the intake packet
- Claim field
- Box 13 (CMS-1500) / 837 assignment indicator
- Medicare
- Participating providers must accept assignment
What does assignment of benefits actually do?
An AOB moves the money. Insurance benefits legally belong to the member; without a signed assignment, the payer's obligation is to the patient, and payment can go to the patient's mailbox. The AOB is the patient saying, in writing, "pay my provider directly." On the CMS-1500 it lives in box 13 ("signature on file"), and in the 837 it is the assignment indicator your PM system sets from the registration record.
Most practices bundle AOB into the intake packet with financial responsibility and HIPAA acknowledgments, signed once and kept on file — which is why the claim says "signature on file" rather than carrying an actual signature.
How does assignment work with Medicare?
Medicare gives "assignment" a second, stricter meaning. A participating provider has agreed in advance to accept assignment on every claim: Medicare pays 80% of the allowed amount directly to the provider, the patient owes the remaining 20%, and the provider cannot bill beyond the allowed amount. Non-participating providers who do not accept assignment are paid at 95% of the fee schedule, payment goes to the patient, and the limiting charge caps what they can bill (115% of the non-PAR amount).
Concrete numbers: if the PAR allowed amount for a service is $100, a non-PAR provider's allowed amount is $95, and the limiting charge is 95 × 1.15 = $109.25 — the absolute ceiling they may charge the beneficiary, with the check going to the patient, not the practice.
What happens when the check goes to the patient?
This is mostly an out-of-network problem. Several large commercial payers pay the member on out-of-network claims as a matter of policy, even with an AOB on the claim, because their view is that the provider has no contract with them. The practice then has to invoice the patient and hope the insurance check was not already spent. Recovery rates on patient-cashed insurance checks are poor, and the collection cost is high.
How do you get AOB right at intake?
- Include AOB language in every intake packet and re-execute it annually — some payers and most attorneys treat stale authorizations skeptically.
- Add authorized-representative language so you can appeal denials on the member's behalf, especially for ERISA plans.
- Verify your PM system sets the assignment flag — a migration or template change that silently flips box 13 will scatter payments to patients for weeks before anyone notices, and the fix shows up as a mystery drop in your clean-claim cash.
- Keep signed AOBs retrievable. When a payer demands proof of assignment two years later, "we cannot find it" costs you the claim.
Frequently asked questions
The payer can issue payment to the patient (the subscriber), and the provider has to collect from the patient afterward. Some patients forward the check; many do not. Out-of-network claims are where this bites hardest, because several large payers pay the member by default regardless of what the claim says.
They are related but distinct. AOB is the patient authorizing direct payment. "Accepting assignment" with Medicare means the provider agrees to accept the Medicare allowed amount as payment in full. Participating (PAR) providers accept assignment on all claims; non-PAR providers can choose per claim but face payment at 95% of the fee schedule.
Often, yes. A well-drafted AOB combined with a designation form gives the provider standing to file claims, receive plan documents, and pursue appeals as the member's authorized representative. For ERISA plans this language matters enormously; without it, plans can refuse to discuss the claim with you.
Sources & further reading
Reviewed by the ImmediCare Solutions RCM team
Certified billers and coders handling claims across 50+ specialties nationwide. This entry is reviewed against current payer policy and CMS rules. Last review: Jul 5, 2026.
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