Free reference
Denial code lookup
Claim adjustment reason codes tell you why a claim was denied — in language written for adjudication systems, not people. This translates the ones you actually see, with the fix and the prevention for each.
190 codes · Last updated August 20, 2026
Most looked-up codes — full guides
CPT modifiers explained →How to use this
Reading a denial properly
A remittance carries two kinds of code. The CARC (Claim Adjustment Reason Code) states the reason for the adjustment. The RARC (Remittance Advice Remark Code) adds detail. The two are meant to be read together, and reading only the CARC is why so many denials get worked incorrectly.
CO-16 is the clearest example. On its own it means only that required information is missing — it tells you nothing about what. The accompanying RARC names the actual field. Practices that work CO-16 denials without reading the RARC end up guessing.
The prefix matters too. CO means contractual obligation, which generally cannot be billed to the patient. PR means patient responsibility, which can. Misreading a CO as a PR and billing the patient is both a collection failure and a contractual problem.
Finally, aggregate them. A single denial is a claim problem; the same reason code appearing forty times a month is a process problem with a specific owner, and that is the one worth fixing.
Stop working the same denial forty times
A free billing audit aggregates your denials by reason code and payer, and tells you which upstream process is generating them.
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