> ## Documentation Index
> Fetch the complete documentation index at: https://www.practiceownersguide.com/llms.txt
> Use this file to discover all available pages before exploring further.

# CARC and RARC: denial codes

> Every dollar a payer doesn't pay arrives with a coded explanation. Reading the codes turns 'insurance shorted us again' into a specific, fixable problem.

Every dollar a payer doesn't pay arrives with a coded explanation. Reading the codes turns "insurance shorted us again" into a specific, fixable problem.

## The grammar

Adjustments in an [835](/concepts/what-is-an-835) have three parts:

* **Group code**: who bears the cost. **CO** (contractual, not billable to patient), **PR** (patient responsibility, billable), **OA**/**PI** (other/payer-initiated). CO vs. PR is the legal line between a write-off and a patient bill.
* **CARC**: why. Maintained by X12 ([x12.org/codes](https://x12.org/codes)).
* **RARC**: supplementary detail refining the CARC.

So `CO-45` reads: contractual obligation, charge exceeds the fee schedule. That's the routine network discount on every claim.

## The field guide

| Code         | Meaning                          | Action                                                    |
| ------------ | -------------------------------- | --------------------------------------------------------- |
| CO-45        | Contract discount                | Nothing, unless paid rate is below contract. Then dispute |
| PR-1/2/3     | Deductible / coinsurance / copay | Bill the patient                                          |
| CO-16 + RARC | Claim lacks information          | Fix per the RARC, resubmit                                |
| CO-29        | Past timely filing               | Appeal only with proof; otherwise fix the upstream delay  |
| CO-50        | Not medically necessary          | Appeal with documentation                                 |
| CO-97        | Bundled into another service     | Check modifiers                                           |
| CO-109       | Wrong payer                      | Coordination of benefits; redirect                        |
| CO-197       | No prior authorization           | Fix scheduling workflow; appeals are uphill               |

## Why owners should care

Denials are a diagnosis of your own front end. CO-16 spikes mean registration gaps. CO-29 means claims sit before submission. CO-197 means scheduling doesn't check auth. Industry surveys put initial denial rates around 10 to 15%, and a large share are never reworked, which is forfeited revenue since most reworked denials pay. You don't have to read codes yourself. You need someone reading them, a monthly denial summary by CARC, and resubmission deadlines.

<Warning>
  Many payers print proprietary codes on paper EOBs that don't map cleanly to CARCs. One more reason to get every payer onto [ERA](/concepts/era-vs-eob).
</Warning>

<Note>
  **Lemma aside:** Lemma parses every remittance, so adjustment codes land as structured, searchable data next to the actual deposit ([docs](https://docs.getlemma.com)).
</Note>