The denial codes list, in plain English

Every common CARC below links to a working page: what the code really means, why it fired, the exact fix steps, and a free AI drafter for the appeal letter. Bookmark this — it's the lookup your ERA work queue deserves.

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CO codes — Contractual Obligation

the provider absorbs it — the amount cannot be billed to the patient. If the denial is wrong, the money is recovered by correcting or appealing the claim, not by balance-billing.

CO 16 — Claim Lacks InformationClaim/service lacks information or has submission/billing error(s) which is needed for adjudication.CO 97 — Bundled Into Another ServiceThe benefit for this service is included in the payment/allowance for another service/procedure that has alrea…CO 45 — Exceeds Fee ScheduleCharge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.CO 96 — Non-Covered ChargesNon-covered charge(s). The related remark code identifies why.CO 22 — Another Payer Is PrimaryThis care may be covered by another payer per coordination of benefits.CO 197 — No Prior AuthorizationPrecertification/authorization/notification absent.CO 4 — Modifier Missing or InconsistentThe procedure code is inconsistent with the modifier used, or a required modifier is missing.CO 29 — Timely Filing ExpiredThe time limit for filing has expired.CO 252 — Documentation RequiredAn attachment/other documentation is required to adjudicate this claim/service.CO 109 — Wrong Payer / ContractorClaim/service not covered by this payer/contractor. You must send the claim/service to the correct payer/contr…CO 24 — Covered by Capitation / Managed CareCharges are covered under a capitation agreement/managed care plan.CO 50 — Not Medically NecessaryThese are non-covered services because this is not deemed a 'medical necessity' by the payer.CO 226 — Provider Info Not ReceivedInformation requested from the Billing/Rendering Provider was not provided or was insufficient/incomplete.CO 234 — Not Paid SeparatelyThis procedure is not paid separately.CO 151 — Frequency / Units ExceededPayment adjusted because the payer deems the information submitted does not support this many/frequency of ser…CO 253 — Sequestration ReductionSequestration - reduction in federal payment.CO 119 — Benefit Maximum ReachedBenefit maximum for this time period or occurrence has been reached.CO 236 — Incompatible Procedure CombinationThis procedure or procedure/modifier combination is not compatible with another procedure or procedure/modifie…CO 59 — Multiple Procedure ReductionProcessed based on multiple or concurrent procedure rules.CO 18 — Duplicate ClaimExact duplicate claim/service.CO 11 — Diagnosis Inconsistent With ProcedureThe diagnosis is inconsistent with the procedure.CO 129 — Prior Processing Info IncorrectPrior processing information appears incorrect.CO 23 — Prior Payer Adjudication ImpactThe impact of prior payer(s) adjudication including payments and/or adjustments.CO 131 — Negotiated DiscountClaim specific negotiated discount.CO B7 — Provider Not Certified for ServiceThis provider was not certified/eligible to be paid for this procedure/service on this date of service.CO 27 — Coverage Terminated (Provider Liability)Expenses incurred after coverage terminated.CO 58 — Wrong Place of ServiceTreatment was deemed by the payer to have been rendered in an inappropriate or invalid place of service.CO 26 — Expenses Before CoverageExpenses incurred prior to coverage.CO 39 — Authorization Denied at RequestServices denied at the time authorization/pre-certification was requested.CO 31 — Patient Not IdentifiedPatient cannot be identified as our insured.CO 167 — Diagnosis Not CoveredThis (these) diagnosis(es) is (are) not covered.CO 170 — Provider Type Cannot Bill ThisPayment is denied when performed/billed by this type of provider.CO 181 — Procedure Code Invalid on DOSProcedure code was invalid on the date of service.CO 198 — Authorization ExceededPrecertification/notification/authorization/pre-treatment exceeded.CO 6 — Age Inconsistent With ProcedureThe procedure/revenue code is inconsistent with the patient's age.CO 146 — Diagnosis Invalid for DateDiagnosis was invalid for the date(s) of service reported.CO 15 — Authorization InvalidThe authorization number is missing, invalid, or does not apply to the billed services or provider.CO 13 — Date of Death Precedes ServiceThe date of death precedes the date of service.

PR codes — Patient Responsibility

the amount can be billed to the patient (deductible, coinsurance, non-covered care) — but only after you verify the denial is correct. Mis-grouped PR denials are a common appeal win.

PR 96 — Non-Covered (Patient Liability)Non-covered charge(s).PR 27 — Coverage Terminated (Patient Liability)Expenses incurred after coverage terminated.PR 204 — Not Covered by Benefit PlanThis service/equipment/drug is not covered under the patient's current benefit plan.PR 31 — Patient Not Identified (PR)Patient cannot be identified as our insured.PR 119 — Benefit Max Reached (Patient Liability)Benefit maximum for this time period or occurrence has been reached.PR 1 — DeductibleDeductible amount.PR 49 — Routine Exam Not CoveredThis is a non-covered service because it is a routine/preventive exam or a diagnostic/screening procedure done…PR 2 — CoinsuranceCoinsurance amount.PR 3 — CopaymentCo-payment amount.

OA codes — Other Adjustment

neither clearly provider nor patient liability — most often coordination-of-benefits math or duplicates. Usually informational; verify before writing anything off.

OA 23 — Prior Payer Adjudication (OA)The impact of prior payer(s) adjudication including payments and/or adjustments. (Use only with Group Code OA)OA 18 — Duplicate (Other Adjustment)Exact duplicate claim/service.

Frequently asked questions

What are CARC denial codes?

Claim Adjustment Reason Codes (CARCs) are the standardized codes payers put on the ERA/EOB to explain why a claim line paid differently than billed. The group prefix (CO/PR/OA/PI) assigns liability; the number gives the reason. Remark codes (RARCs) add detail.

What's the difference between CO, PR and OA?

CO = Contractual Obligation (provider absorbs it, patient cannot be billed). PR = Patient Responsibility (billable to the patient once verified). OA = Other Adjustment (neither — usually COB math or duplicates). The same number can appear under different groups with very different consequences.

Which denial codes are worth appealing?

Medical necessity (CO 50), bundling (CO 97), prior auth (CO 39/197), timely filing with proof (CO 29), and benefit-category errors (CO 96/PR 204) reverse most often. Mechanical codes — CO 16, CO 146, CO 181 — are corrected-claim territory, not appeals.