Denial Code Lookup & Decoder
Look up any medical-billing denial code (CARC or RARC) — what it means, why you got it, and how to fix or appeal it. Or paste a remittance and decode every code at once.
The best denial is no denial.
Most coding-driven denials — bundling, medical necessity, missing codes — are preventable. CodeSightTM catches them before the claim goes out.
How denial codes actually work
Every adjustment on an EOB or 835 remittance stacks three things: a group code (who pays), a CARC (the reason), and sometimes a RARC (extra detail).
Frequently Asked Questions
A CARC (Claim Adjustment Reason Code) tells you why a claim or line was adjusted — for example CO-45 (charge exceeds the allowed amount) or CO-50 (not medically necessary). A RARC (Remittance Advice Remark Code, such as N130 or M76) is supplemental: it adds detail to a CARC but rarely stands alone. Read the CARC first for the reason, then use any RARC for the specifics.
The two-letter group code tells you who is responsible for the adjusted amount. CO = Contractual Obligation (the provider writes it off). PR = Patient Responsibility (billable to the patient). OA = Other Adjustment. PI = Payer-Initiated Reductions. CR = Corrections and Reversal. The group code is why CO-45 cannot be billed to the patient but PR-1 can.
Yes. CARC and RARC codes are published openly by X12 and CMS because they are required in the HIPAA-mandated electronic remittance (835) transaction. The codes themselves are public. Medmio's plain-English explanations are original and free to use for reference.
Yes. The decoder runs entirely in your browser — anything you paste is parsed on your own device and is never uploaded, stored, or sent to any server. You only need the codes and amounts to decode them, so there's no reason to paste patient names, dates of birth, member IDs, or other protected health information (PHI).
The CARC and RARC code sets are updated three times a year, with changes typically effective in March, July, and November. New codes are added and others are deactivated. Always confirm against the latest X12 and CMS release for active status.
Yes. Each code page explains what the denial means, the common causes, step-by-step how to fix it, how to prevent it, and — where the denial is appealable — a copy-ready appeal letter template you can fill in and send.