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 |
|---|---|---|
| N399 | Incomplete/invalid elective consent form. | Details → |
| N4 | Missing/Incomplete/Invalid prior Insurance Carrier(s) EOB. | Details → |
| N4 | Missing/Incomplete/Invalid prior Insurance Carrier(s) EOB. | Details → |
| N40 | Missing radiology film(s)/image(s). | Details → |
| N40 | Missing radiology film(s)/image(s). | Details → |
| N400 | Alert: Electronically enabled providers should submit claims electronically. | Details → |
| N400 | Alert: Electronically enabled providers should submit claims electronically. | Details → |
| N401 | Missing periodontal charting. | Details → |
| N401 | Missing periodontal charting. | Details → |
| N402 | Incomplete/invalid periodontal charting. | Details → |
| N402 | Incomplete/invalid periodontal charting. | Details → |
| N403 | Missing facility certification. | Details → |
| N403 | Missing facility certification. | Details → |
| N404 | Incomplete/invalid facility certification. | Details → |
| N404 | Incomplete/invalid facility certification. | Details → |
| N405 | This service is only covered when the donor's insurer(s) do not provide coverage for … | Details → |
| N405 | This service is only covered when the donor's insurer(s) do not provide coverage for … | Details → |
| N406 | This service is only covered when the recipient's insurer(s) do not provide coverage … | Details → |
| N406 | This service is only covered when the recipient's insurer(s) do not provide coverage … | Details → |
| N407 | You are not an approved submitter for this transmission format. | Details → |
| N407 | You are not an approved submitter for this transmission format. | Details → |
| N408 | This payer does not cover deductibles assessed by a previous payer. | Details → |
| N408 | This payer does not cover deductibles assessed by a previous payer. | Details → |
| N409 | This service is related to an accidental injury and is not covered unless provided wi… | Details → |
| N409 | This service is related to an accidental injury and is not covered unless provided wi… | Details → |
| N41 | Authorization request denied. | Details → |
| N41 | Authorization request denied. | Details → |
| N410 | Not covered unless the prescription changes. | Details → |
| N410 | Not covered unless the prescription changes. | Details → |
| N411 | This service is allowed one time in a 6-month period. | Details → |
| N411 | This service is allowed one time in a 6-month period. | Details → |
| N412 | This service is allowed 2 times in a 12-month period. | Details → |
| N412 | This service is allowed 2 times in a 12-month period. | Details → |
| N413 | This service is allowed 2 times in a benefit year. | Details → |
| N413 | This service is allowed 2 times in a benefit year. | Details → |
| N414 | This service is allowed 4 times in a 12-month period. | Details → |
| N414 | This service is allowed 4 times in a 12-month period. | Details → |
| N415 | This service is allowed 1 time in an 18-month period. | Details → |
| N415 | This service is allowed 1 time in an 18-month period. | Details → |
| N416 | This service is allowed 1 time in a 3-year period. | Details → |
| N416 | This service is allowed 1 time in a 3-year period. | Details → |
| N417 | This service is allowed 1 time in a 5-year period. | Details → |
| N417 | This service is allowed 1 time in a 5-year period. | Details → |
| N418 | Misrouted claim. See the payer's claim submission instructions. | Details → |
| N418 | Misrouted claim. See the payer's claim submission instructions. | Details → |
| N418 | Claim was billed to incorrect contractor For date of service submitted, beneficiary … | Details → |
| N419 | Claim payment was the result of a payer's retroactive adjustment due to a retroactive… | Details → |
| N419 | Claim payment was the result of a payer's retroactive adjustment due to a retroactive… | Details → |
| N42 | Missing mental health assessment. | Details → |
| N42 | Missing mental health assessment. | Details → |
| N420 | Claim payment was the result of a payer's retroactive adjustment due to a Coordinatio… | Details → |
| N420 | Claim payment was the result of a payer's retroactive adjustment due to a Coordinatio… | Details → |
| N421 | Claim payment was the result of a payer's retroactive adjustment due to a review orga… | Details → |
| N421 | Claim payment was the result of a payer's retroactive adjustment due to a review orga… | Details → |
| N422 | Claim payment was the result of a payer's retroactive adjustment due to a payer's con… | Details → |
| N422 | Claim payment was the result of a payer's retroactive adjustment due to a payer's con… | Details → |
| N423 | Claim payment was the result of a payer's retroactive adjustment due to a non standar… | Details → |
| N423 | Claim payment was the result of a payer's retroactive adjustment due to a non standar… | Details → |
| N424 | Patient does not reside in the geographic area required for this type of payment. | Details → |
| N424 | Patient does not reside in the geographic area required for this type of payment. | 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.