What are CARC denial codes?

Claim Adjustment Reason Codes (CARCs) are the standardized codes payers use on remittances to explain why a claim was denied, adjusted or reduced. Group codes prefix them: CO (contractual obligation), PR (patient responsibility), OA (other adjustment), PI (payer-initiated). RARC remark codes add detail.

What is the difference between CO and PR denial codes?

CO (contractual obligation) means the provider absorbs the adjustment and generally cannot bill the patient. PR (patient responsibility) means the amount can be billed to the patient — deductibles, coinsurance, copays and properly noticed non-covered services.

Which denial codes can be appealed?

Most denials are appealable with the right evidence: CO-50 medical necessity denials with clinical documentation, CO-29 timely filing with proof of original submission, CO-97 bundling with modifier justification, and CO-197 authorization denials via retro-auth requests. Pure contractual adjustments like CO-45 are generally not appealable unless the allowed amount breaches your contract.

Free tool · 38 codes decoded

Denial Code Lookup

Type any CARC denial code from your remittance — CO-45, CO-29, PR-1, or just the number — and get what it actually means: the cause, the fix, whether it's appealable, and how to stop it happening again. You can also search by problem: try "duplicate", "auth" or "timely".

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No match for that code yet. This tool covers the 38 most common CARC codes — if you're seeing something rarer, the remittance RARC remark usually explains it, or send it to us and we'll decode it (and add it here).

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Go deeper

Full guides: Top 10 denial codes · CO-29 timely filing · CO-45 contractual · CO-50 medical necessity · How to reduce denials. Payer appeal guides: UnitedHealthcare · Aetna · Cigna · BCBS · Humana.