Claim adjustment reason code
Denial code CO-21 meaning
CARC 21, usually seen as CO-21: The payer sees this as covered by a no-fault or auto insurance carrier.
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- Reason code
- CARC 21
- Short name
- No-fault carrier should pay
- Plain meaning
- The payer sees this as covered by a no-fault or auto insurance carrier.
- Group codes
- CO-21: Contractual obligation. The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
Plain-English summary written by Rivvi. X12 owns the CARC list and its exact wording, which is not reproduced here. Read it on the X12 CARC list (list dated November 1, 2025, checked October 23, 2026). This page does not decide how a claim is paid.
Common causes
- The claim shows an auto accident.
What to check before resubmitting
- Bill the auto or no-fault carrier first.
- Send that carrier's payment or denial to this payer if they are secondary.
Related reason codes
Related pages
Questions
What does denial code CO-21 mean?
The payer sees this as covered by a no-fault or auto insurance carrier. This is Rivvi's plain-English summary of CARC 21. X12's exact wording is on x12.org.
How do I fix CO-21?
Bill the auto or no-fault carrier first. Send that carrier's payment or denial to this payer if they are secondary.
Can I bill the patient for CO-21?
With group code CO, no. CO means the provider absorbs the amount under its contract or the payer's rules.
Which group codes come with CARC 21?
Most often CO (contractual obligation). The group code, not the reason code, says who owes the amount.
What is the difference between a CARC and a RARC?
A claim adjustment reason code (CARC) says why a claim line was paid differently than billed. A remittance advice remark code (RARC) adds detail, such as which field is missing.