19 Denial Codes Explained

Insurance Denial Codes —
What They Mean and How to Fight Back

Find your denial code below. Each guide explains exactly what it means, why you received it, and your strongest arguments for appeal.

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Medical Necessity & Coverage Denials

The most common denial category — and the most frequently overturned.

CO-50 Not Medically Necessary The most common denial code in the US. Frequently reversed with proper documentation. Read guide → CO-167 Diagnosis Not Covered Your insurer denied based on the diagnosis category rather than the procedure itself. Read guide → CO-204 Drug or Equipment Not Covered The medication or device is not on your plan's formulary or covered equipment list. Read guide →

Billing & Coding Errors

Administrative errors the provider or insurer must fix — not you.

CO-4 Procedure / Modifier Mismatch The procedure code conflicts with the modifier. A billing error requiring corrected resubmission. Read guide → CO-11 Diagnosis Inconsistent With Procedure The ICD-10 code does not align with the billed CPT procedure code. Read guide → CO-16 Missing or Invalid Information The claim is missing required information. Always comes with a remark code identifying the specific issue. Read guide → CO-58 Invalid Place of Service The place of service code does not match where care was actually delivered. Read guide → CO-109 Claim Sent to Wrong Payer The claim was submitted to the incorrect insurance company. Common in coordination of benefits situations. Read guide → CO-B7 Provider Not Certified The rendering provider is not credentialed or enrolled with the payer for this service. Read guide →

Filing & Timing Issues

Deadline and sequencing denials — often challengeable when the error was the provider's.

CO-29 Timely Filing Exceeded The claim was submitted after the plan's filing deadline. Frequently a provider billing error. Read guide → B15 Qualifying Service Not Yet Adjudicated Payment is on hold until a related prerequisite service is processed first. Read guide →

Coverage & Eligibility Denials

Coverage period disputes and benefit limit issues.

CO-26 Coverage Not Yet Effective The service date falls before your coverage start date. Often a billing or enrollment error. Read guide → CO-27 Coverage Terminated Before Care The service date falls after your coverage end date. Challengeable when termination was improper. Read guide → CO-119 Benefit Maximum Reached You have hit the annual benefit cap. Mental health caps may violate federal parity law. Read guide → CO-151 Frequency Limit Exceeded The service was provided more often than your plan allows within a given timeframe. Read guide →

Authorization & Patient Billing

Charges that are frequently not your responsibility to pay.

CO-197 Prior Authorization Missing No prior auth was obtained. If your provider is in-network, they — not you — bear this responsibility. Read guide → PR-96 Non-Covered Charge The service falls outside covered benefits. Only enforceable when the exclusion is clearly stated. Read guide → PR-97 Bundled Charge Billed to You A bundled service was incorrectly billed to you. In-network providers must write this off. Read guide → OA-23 Coordination of Benefits Adjustment Adjusted based on what your primary insurer paid. You are not responsible for the gap. Read guide →

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