CARCs explain why a claim or line was paid differently than billed. RARCs add detail about what to do next. Together with a group code, they are the language every remittance uses. Learn to read them and most denials tell you their own fix.
1. What CARC and RARC codes are
- CARC (Claim Adjustment Reason Code): the reason for an adjustment, such as "deductible", "duplicate claim", or "time limit for filing has expired". Every adjustment on a remittance carries one.
- RARC (Remittance Advice Remark Code): supplemental information, such as which field is missing or which policy was applied. RARCs start with M, MA, or N. CMS maintains the RARC list.
Both lists are published through X12 and updated several times a year. Codes are added, revised, and retired, so billing systems need current lists.
2. Group codes: CO, PR, OA, PI
| Group code | Stands for | What it means for billing |
|---|---|---|
| CO | Contractual Obligation | Provider responsibility. Cannot be billed to the patient. |
| PR | Patient Responsibility | Can be billed to the patient or a secondary payer. |
| OA | Other Adjustment | Used when neither CO nor PR applies, for example some coordination of benefits adjustments. |
| PI | Payer Initiated Reduction | A reduction the payer made that is not a contractual obligation and not the patient's responsibility. |
Read the group code first. The same CARC can mean very different things for collections: CO-50 is a provider write-off or appeal, while PR-50 can be billed to the patient.
3. Where they appear on the 835
- CARCs appear in CAS segments, at the claim level (loop 2100) and the service line level (loop 2110), with the group code and amount.
- RARCs appear in LQ segments at the service line level, and in MIA or MOA segments at the claim level.
If your team reads paper or PDF remittances, these show up as columns next to each line. Our 835 payment posting guide goes deeper on the file.
4. Common CARC codes
| CARC | Plain-English meaning | Usual next step |
|---|---|---|
| 1 | Deductible amount | Bill patient or secondary. PR-1 guide |
| 2 | Coinsurance amount | Bill patient or secondary. |
| 3 | Copayment amount | Bill patient or secondary. |
| 4 | Procedure code inconsistent with the modifier, or modifier missing | Fix the modifier and send a corrected claim. |
| 5 | Procedure code or bill type inconsistent with place of service | Correct the place of service or bill type. |
| 11 | Diagnosis inconsistent with the procedure | Review coding against the record. |
| 16 | Claim lacks information or has a billing error | Read the remark code, fix, resubmit. CO-16 guide |
| 18 | Exact duplicate claim or service | Check status of the original claim. Do not resubmit. |
| 22 | May be covered by another payer (coordination of benefits) | Confirm primary coverage and bill in the right order. |
| 23 | Impact of prior payer adjudication | Usually informational on secondary claims. |
| 27 | Expenses incurred after coverage terminated | Verify coverage dates; find current coverage. |
| 29 | Time limit for filing has expired | Appeal only with proof of timely filing. Timely filing guide |
| 31 | Patient cannot be identified as the payer's insured | Verify member ID and demographics. |
| 45 | Charge exceeds fee schedule or contracted amount | Contractual write-off. Check the allowed amount against your contract. |
| 50 | Not medically necessary per the payer | Fix coding or appeal with documentation. CO-50 guide |
| 96 | Non-covered charge | Check benefits; bill patient only if allowed. |
| 97 | Included in payment for another service (bundled) | Check edits and modifiers. CO-97 guide |
| 109 | Not covered by this payer; send to the correct payer | Find the right payer and rebill. |
| 119 | Benefit maximum reached for the period or occurrence | Check benefits; bill secondary or patient if allowed. |
| 151 | Information does not support this many or this frequency of services | Review units and frequency; appeal with documentation. |
| 167 | Diagnosis not covered | Review diagnosis coding and coverage policy. |
| 181 | Procedure code invalid on the date of service | Use a code valid for that date. |
| 185 | Rendering provider not eligible to perform the service billed | Check credentialing and scope. |
| 197 | Precertification or authorization absent | Find or request authorization; appeal if it existed. |
| 204 | Not covered under the patient's current benefit plan | Check benefits; bill patient if allowed. |
| 242 | Services not provided by network or primary care providers | Check network status and referral rules. |
| 252 | Attachment or other documentation required | Send the requested documentation. |
About the code descriptionsDescriptions on this page are plain-English summaries. The official wording lives in the CARC and RARC code lists published through X12 (and by CMS for remark codes), which are updated several times a year. Check the current list before quoting a code in an appeal.
5. Common RARC codes
| RARC | Plain-English meaning |
|---|---|
| MA130 | Claim was unprocessable because of incomplete or invalid information. Submit a new claim; no appeal rights. |
| M51 | Missing, incomplete, or invalid procedure code. |
| M76 | Missing, incomplete, or invalid diagnosis. |
| N290 | Missing, incomplete, or invalid rendering provider identifier. |
| N382 | Missing, incomplete, or invalid patient identifier. |
| M15 | Separately billed services were bundled as components of the same procedure. |
| M80 | Not covered when performed during the same session or date as another service. |
| N115 | Decision based on a Local Coverage Determination (LCD). |
| N386 | Decision based on a National Coverage Determination (NCD). |
| N130 | Consult plan benefit documents for restrictions on this service. |
| N30 | Patient ineligible for this service. |
| MA04 | Secondary payment cannot be considered without primary payer information. |
| MA18 | Claim information was forwarded to the patient's supplemental insurer. |
6. How to use CARC and RARC data to cut denials
- Export 90 days of remittance adjustments with group code, CARC, RARC, payer, CPT, and provider.
- Leave out the routine ones (PR-1, PR-2, PR-3, CO-45) and rank the rest by dollars.
- Group by root cause, not by code. CO-16 with N290 and CO-185 might both trace back to provider enrollment.
- Fix the top three causes upstream: scrubber edits, eligibility checks, enrollment, or documentation.
- Re-run the same report monthly and track dollars denied per cause.
For a Medicare-specific view, see our Medicare denial codes reference. For the recovery workflow, see the denial recovery playbook.
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What is the difference between a CARC and a RARC?
A CARC explains why a claim or line was adjusted. A RARC adds supporting detail, such as which field was missing or which policy applied. A remittance can include a CARC alone, but many CARCs, like 16, require a RARC.
What do the group codes CO, PR, OA, and PI mean?
CO is contractual obligation (provider responsibility), PR is patient responsibility, OA is other adjustment, and PI is a payer-initiated reduction. The group code tells you who owns the unpaid amount.
Who maintains CARC and RARC codes?
CARCs are maintained by a code maintenance committee and published through X12. RARCs are maintained by CMS and also published through X12. Both are updated several times a year.
Where do I find the official CARC and RARC list?
The current lists are published on the X12 website. CMS also publishes RARC updates. Billing software should load the current lists automatically.
What are the most common denial codes?
Frequent ones include CO-16 (missing information), CO-97 (bundled), CO-50 (medical necessity), CO-197 (no authorization), CO-29 (timely filing), CO-18 (duplicate), and CO-22 (coordination of benefits). Which ones dominate depends on your specialty and payer mix.
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