VerifyDoc / Free Tools / Denial Code Decoder
Free tool

What does this denial code mean?

Enter a code from your explanation of benefits. You will get what it means in plain English, and — more usefully — whether that amount can be billed to you at all.

On most EOBs this is the two letters printed just before the number.
Type the code as it appears — "CO-45", "45", or a RARC like "MA130" all work.

The two letters matter more than the number

Every adjustment line on an explanation of benefits carries a group code, and it answers the only question that really matters: can this amount be billed to you at all?

CO — contractual obligation. The provider agreed to this reduction when they joined the insurer's network. It is written off, and it is not yours. A CO amount appearing on a patient bill is the most common form of improper balance billing.

PR — patient responsibility. Genuinely assigned to you: deductible, copay, coinsurance, or a non-covered service. Still worth checking the arithmetic, because it is calculated from the allowed amount.

OA and PI. Other adjustments and payer-initiated reductions. Neither is normally patient responsibility, and OA usually signals a coordination-of-benefits problem — the claim went to the wrong insurer first.

The highest-value check on any medical bill takes about a minute. Put your EOB next to the bill from the provider. The EOB's "patient responsibility" figure is what you owe. If the provider's bill is higher, the difference is usually a CO amount that should have been written off — and that single comparison catches more money than any other check a patient can do unaided.

A denial is not a final answer

A large share of denials are administrative rather than substantive — a missing modifier, a stale coordination-of-benefits record, a claim sent to the wrong payer, a filing deadline the provider missed. None of those are judgments about your care, and most are resolved by the provider resubmitting rather than by you paying.

Where a denial is substantive, you have appeal rights, and the deadlines are strict. Ask the insurer in writing for the specific plan provision relied on. Request the claim be reprocessed rather than merely reviewed. And keep the paper: dates, names, reference numbers.

Coverage note. This decoder covers the codes patients see most often, written in plain English. It is not the complete list — the full CARC and RARC sets run to several hundred codes and are maintained externally. If your code is not here, the authoritative lists are published at x12.org/codes.

One code is a clue. The whole bill is the case.

VerifyDoc reads your entire itemised bill and EOB together — every line, every code, every amount that should have been written off — and tells you in plain English what to dispute and why.

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Not medical, legal, or billing advice. Code meanings are summarised in plain English and are not the official descriptor text. Whether a specific amount is billable depends on your plan documents, your provider's network status, and applicable state and federal law. Verify against your own EOB and plan before acting.