Group code CO — Contractual Obligation
Contractual write-off. The provider agreed to the rate. Patient does NOT owe this amount.
Contractual Obligation (CO) is the largest group of adjustments on a typical EOB. It means the provider agreed, by being in-network or by signing a fee schedule, to accept the insurer's allowed amount as full payment. The difference between the billed amount and the allowed amount is the contractual write-off — the patient does not owe it. If the provider tries to balance-bill the patient for a CO adjustment, the patient has strong protections under state network-adequacy laws and federal No Surprises Act provisions for emergency or surprise out-of-network care.
How group code CO appears on your EOB
Every adjustment line on an insurance Explanation of Benefits (or 835 Electronic Remittance Advice) has a group code and at least one reason code (CARC). The group code is the “who”: CO means Contractual Obligation. The CARC is the “why”: a specific numeric reason like 50 (not medically necessary), 197 (prior auth absent), or 204 (not covered under benefit plan).
All four group codes
For context, the four X12 adjustment group codes are:
- CO — Contractual Obligation: Contractual write-off. The provider agreed to the rate. Patient does NOT owe this amount.
- PR — Patient Responsibility: Patient owes this amount. Deductibles, coinsurance, copays, and excluded benefits land here.
- OA — Other Adjustment: Informational or coordination-related adjustment. Usually means another payer is involved or there's a non-claim-related accounting entry.
- PI — Payer Initiated Reductions: Payer reduced the payment for a reason that is neither contractual nor patient responsibility. Often appealable.
Frequently asked questions
Do I owe the CO adjustment amount?
No. CO (Contractual Obligation) is the difference between the provider's billed amount and the insurer's allowed amount. The provider agreed to write off this difference as part of their in-network contract. If a provider tries to balance-bill you for a CO amount, contact your state insurance department — this is typically prohibited.
Can I appeal a CO adjustment?
Usually not — the CO amount is set by the contract between the provider and the insurer, not by your benefits. But if a clinical denial appears in the CO group (like CO-50 medical-necessity or CO-197 prior-auth-absent), you absolutely can appeal the denial itself even though the adjustment lands under CO.
Why do most denials appear under CO?
Because most US healthcare claims flow through in-network providers. The CO group captures the contractual relationship: the provider is in-network, agreed to a rate, and any adjustment to that rate is contractual rather than the patient's responsibility.
Common CARC codes under group CO
- CARC 4 — The procedure code is inconsistent with the modifier used.Typically appealable
- CARC 5 — The procedure code/type of bill is inconsistent with the pla…Typically appealable
- CARC 6 — The procedure/revenue code is inconsistent with the patient'…Typically appealable
- CARC 7 — The procedure/revenue code is inconsistent with the patient'…Typically appealable
- CARC 8 — The procedure code is inconsistent with the provider type/sp…Typically appealable
- CARC 9 — The diagnosis is inconsistent with the patient's age.Typically appealable
- CARC 10 — The diagnosis is inconsistent with the patient's gender.Typically appealable
- CARC 11 — The diagnosis is inconsistent with the procedure.Typically appealable
- CARC 12 — The diagnosis is inconsistent with the provider type.Typically appealable
- CARC 13 — The date of death precedes the date of service.
Sources
Contact: hello@approvalhelp.com