Claim adjustment reason code
Denial code CO-B4 meaning
CARC B4, usually seen as CO-B4: A penalty was taken because the claim was filed late.
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- Reason code
- CARC B4
- Short name
- Late filing penalty
- Plain meaning
- A penalty was taken because the claim was filed late.
- Group codes
- CO-B4: 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 was filed after the payer's deadline, and the payer reduces rather than denies late claims.
What to check before resubmitting
- File claims within the deadline.
Related reason codes
Related pages
Questions
What does denial code CO-B4 mean?
A penalty was taken because the claim was filed late. This is Rivvi's plain-English summary of CARC B4. X12's exact wording is on x12.org.
How do I fix CO-B4?
File claims within the deadline.
Can I bill the patient for CO-B4?
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 B4?
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.