Instantly find explanations, causes, and resolution steps for every Claim Adjustment Reason Code (CARC) and Remark Code.
Claim Adjustment Reason Codes (CARC) explain why a payment differs from what was billed. Every 835 ERA and EOB uses these standardized codes.
Search any code or keyword above. Each page includes the full description, common causes, resolution steps, and appeal guidance.
Each denial code page also links to a dedicated Remark Code page — optimized for providers searching for ERA remark code context.
Most denials are reversible. Our guides walk you through the correct steps to correct, resubmit, or formally appeal each denial type.
| Code | Description | View |
|---|---|---|
| N636 | Adjusted because this is reimbursable only once per injury. | Details → |
| N637 | Consultations are not allowed once treatment has been rendered by the same provider. | Details → |
| N637 | Consultations are not allowed once treatment has been rendered by the same provider. | Details → |
| N638 | Reimbursement has been made according to the home health fee schedule. | Details → |
| N638 | Reimbursement has been made according to the home health fee schedule. | Details → |
| N639 | Reimbursement has been made according to the inpatient rehabilitation facilities fee … | Details → |
| N639 | Reimbursement has been made according to the inpatient rehabilitation facilities fee … | Details → |
| N64 | The 'from' and 'to' dates must be different. | Details → |
| N64 | The 'from' and 'to' dates must be different. | Details → |
| N640 | Exceeds number/frequency approved/allowed within time period. | Details → |
| N640 | Exceeds number/frequency approved/allowed within time period. | Details → |
| N641 | Reimbursement has been based on the number of body areas rated. | Details → |
| N641 | Reimbursement has been based on the number of body areas rated. | Details → |
| N642 | Adjusted when billed as individual tests instead of as a panel. | Details → |
| N642 | Adjusted when billed as individual tests instead of as a panel. | Details → |
| N643 | The services billed are considered Not Covered or Non-Covered (NC) in the applicable … | Details → |
| N643 | The services billed are considered Not Covered or Non-Covered (NC) in the applicable … | Details → |
| N644 | Reimbursement has been made according to the bilateral procedure rule. | Details → |
| N644 | Reimbursement has been made according to the bilateral procedure rule. | Details → |
| N645 | Mark-up allowance. | Details → |
| N645 | Mark-up allowance. | Details → |
| N646 | Reimbursement has been adjusted based on the guidelines for an assistant. | Details → |
| N646 | Reimbursement has been adjusted based on the guidelines for an assistant. | Details → |
| N647 | Adjusted based on diagnosis-related group (DRG). | Details → |
| N647 | Adjusted based on diagnosis-related group (DRG). | Details → |
| N648 | Adjusted based on Stop Loss. | Details → |
| N648 | Adjusted based on Stop Loss. | Details → |
| N649 | Payment based on invoice. | Details → |
| N649 | Payment based on invoice. | Details → |
| N65 | Procedure code or procedure rate count cannot be determined, or was not on file, for … | Details → |
| N65 | Procedure code or procedure rate count cannot be determined, or was not on file, for … | Details → |
| N650 | This policy was not in effect for this date of loss. No coverage is available. | Details → |
| N650 | This policy was not in effect for this date of loss. No coverage is available. | Details → |
| N651 | No Personal Injury Protection/Medical Payments Coverage on the policy at the time of … | Details → |
| N651 | No Personal Injury Protection/Medical Payments Coverage on the policy at the time of … | Details → |
| N652 | The date of service is before the date of loss. | Details → |
| N652 | The date of service is before the date of loss. | Details → |
| N653 | The date of injury does not match the reported date of loss. | Details → |
| N653 | The date of injury does not match the reported date of loss. | Details → |
| N654 | Adjusted based on achievement of maximum medical improvement (MMI). | Details → |
| N654 | Adjusted based on achievement of maximum medical improvement (MMI). | Details → |
| N655 | Payment based on provider's geographic region. | Details → |
| N655 | Payment based on provider's geographic region. | Details → |
| N656 | An interest payment is being made because benefits are being paid outside the statuto… | Details → |
| N656 | An interest payment is being made because benefits are being paid outside the statuto… | Details → |
| N657 | This should be billed with the appropriate code for these services. | Details → |
| N657 | This should be billed with the appropriate code for these services. | Details → |
| N658 | The billed service(s) are not considered medical expenses. | Details → |
| N658 | The billed service(s) are not considered medical expenses. | Details → |
| N659 | This item is exempt from sales tax. | Details → |
| N659 | This item is exempt from sales tax. | Details → |
| N66 | Missing/incomplete/invalid documentation. | Details → |
| N66 | Missing/incomplete/invalid documentation. | Details → |
| N660 | Sales tax has been included in the reimbursement. | Details → |
| N660 | Sales tax has been included in the reimbursement. | Details → |
| N661 | Documentation does not support that the services rendered were medically necessary. | Details → |
| N661 | Documentation does not support that the services rendered were medically necessary. | Details → |
| N662 | Alert: Consideration of payment will be made upon receipt of a final bill. | Details → |
| N662 | Alert: Consideration of payment will be made upon receipt of a final bill. | Details → |
| N663 | Adjusted based on an agreed amount. | Details → |
Medical claim denial codes — formally known as Claim Adjustment Reason Codes (CARC) — are standardized identifiers maintained by the X12 standards body and used across all Medicare, Medicaid, and commercial payer 835 electronic remittance transactions. When a claim is paid at a different amount than billed, at least one CARC code must accompany the remittance advice to indicate the specific reason for the adjustment.
The most frequently encountered codes include CO-16 (missing or invalid claim information), CO-45 (charges exceeding fee schedule), PR-1 (patient deductible), CO-29 (timely filing deadline exceeded), and CO-4 (procedure code inconsistent with modifier). Each represents a distinct, actionable reason that has a defined resolution pathway.