Claim adjustment reason code (CARC)
Updated September 30, 2026
Definition
A standard code that explains why your health plan paid a claim line differently than the provider billed it, such as an amount applied to your deductible or a denial.
A claim adjustment reason code (CARC) explains why your health plan paid a claim line differently than the provider billed it. The codes are standard across plans and kept by X12, a national standards group. Some explanation of benefits (EOB) forms show them as a number, often with 2 letters in front.
The letters tell you who's responsible for the gap. CO means contractual obligation, which usually means the provider writes it off. PR means patient responsibility, the part you may owe. OA means other adjustment.
For example, say your EOB shows PR-1 for $150 and CO-45 for $400. Code 1 means the $150 went to your deductible, so you may owe it. Code 45 means the charge was above your plan's allowed fee, so an in-network provider writes off the $400. See denial codes on your EOB for more codes and what to do next.
Related terms
Guides that use this term
- GuideDenial codes on your EOB, explainedWhat do CO-45, PR-1, and CO-16 mean? Look up common claim denial codes, learn who's responsible for each amount, and see what to do about each one.
- GuideInsurance didn't pay my medical bill: what to do nextInsurance didn't pay your medical bill? Find out why, match the denial code to the fix, and learn when to ask for a rebill and when to file an appeal.
Sources
- Claim adjustment reason codes, X12. Accessed September 30, 2026.
This is general information, not legal or medical advice. Rules can depend on your plan and your state. Romi Care isn't an insurer, law firm, collection agency, or government program.