CO 301 denial code

Claim adjustment reason code 301. Often reported as CO 301 or OA 301.

Medical plan: bill the behavioral plan

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 301 means

Send this service to the patient's behavioral health plan; the medical plan says it is not a medical benefit there.

The medical payer says mental health or substance use services belong with the patient's behavioral health plan, often a separate carve out vendor. The claim was not forwarded, so you need to submit it. Code 300 is the forwarded version.

Check the behavioral health plan's network and authorization rules before you bill.

Group codes seen with 301

On a remittance, 301 comes after a group code. These are the ones it is most often reported with:

• CO 301 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.
• OA 301 (Other Adjustment): Used for adjustments that are neither the provider's contractual write-off nor the patient's share. It often appears with coordination of benefits, for example when another payer already paid.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• Behavioral health services were billed to the medical plan.
• The behavioral benefits are managed by a separate vendor.
• The office did not identify the carve out when checking eligibility.

What to do next

1. Identify the patient's behavioral health plan from the ID card or eligibility response.
2. Get any authorization the behavioral health plan requires.
3. Submit the claim to the behavioral health plan with its required format.

Related codes

• 300 (reason code) Medical plan forwarded to behavioral plan