CARC 18: Exact duplicate claim or service
The payer believes this claim or line was already submitted and processed.
Group code context
Usually sent with group code CO (contractual obligation): under your contract you cannot bill the patient for this amount.
Common causes
- Claim resubmitted while the first one was still in process
- Corrected claim sent as a new claim instead of a replacement
- Same service on the same day billed twice without a modifier
Step-by-step fix
- Check claim history to see if the original was paid or denied
- If the original is still open, wait for it
- If you meant to correct it, resubmit with the correct frequency code and original claim number
- If two services really happened, add the right modifier (for example 76 or 77) and documentation
Appeal guidance
Appeal if the services were distinct and supported, with notes showing both.
When not to appeal
Do not appeal a true duplicate.
Prevention checklist
- Check claim status before resubmitting
- Use frequency code 7 with the original claim number for corrections
Related codes
Explain this reference
Get a concise explanation drawn only from this reviewed page. Do not enter patient information.
Source and review
Official source ↗Last checked: 2026-10-05
Reviewed by: PracticeVendors editorial team
Educational reference. Confirm payer instructions and applicable contracts before taking action.