Official CARC description: “The impact of prior payer(s) adjudication including payments and/or adjustments.” Here’s what it actually means, why it fires, and how to get the claim paid.
A secondary-claim code: this payer reduced its payment because of what the primary already paid/adjusted. It's the COB math line, not a denial — audit it rather than appeal it.
Liability group: CO = Contractual Obligation — the provider absorbs it — the amount cannot be billed to the patient. If the denial is wrong, the money is recovered by correcting or appealing the claim, not by balance-billing.
Also written: CO-23, CO23, “denial code 23”, “23 denial code” or “reason code 23” — same CARC, different ERA formatting.
Reason code 23 also appears under another group on the ERA. The number is the reason; the prefix decides who absorbs the money. This page covers CO 23 (Contractual Obligation). If your ERA shows a different prefix, use the matching page:
Verify the primary payment/adjustment amounts transmitted correctly
Check the secondary's allowed-amount logic against its COB method (full vs non-duplication)
If primary data was wrong: corrected secondary claim with accurate COB fields
Post to the right adjustment buckets so patient statements stay correct
Appeal only when the secondary applied the wrong COB methodology for the plan type — attach both EOBs and the plan's COB provision.
Fill in the denial facts — use placeholders, never real patient data (the letter keeps [PATIENT NAME]-style fields so you can merge real details privately). A payer-ready draft with an enclosure checklist comes back in ~20 seconds.
Your appeal letter draft will appear here.
The official CARC description for CO 23 is: “The impact of prior payer(s) adjudication including payments and/or adjustments.” In practice: A secondary-claim code: this payer reduced its payment because of what the primary already paid/adjusted. It's the COB math line, not a denial — audit it rather than appeal it.
Denial code 23 under the CO group (Contractual Obligation) means: The impact of prior payer(s) adjudication including payments and/or adjustments. The number is the reason; the CO prefix decides who is liable — the provider absorbs it — the amount cannot be billed to the patient. If the denial is wrong, the money is recovered by correcting or appealing the claim, not by balance-billing.
Yes. CO 23, CO-23, CO23 and “denial code 23” are the same CARC — clearinghouses, payer portals and PM systems just print it differently. Only the group prefix (CO, PR, OA or PI) changes the meaning, because it changes who has to absorb the amount.
CO stands for Contractual Obligation — the provider absorbs it — the amount cannot be billed to the patient. If the denial is wrong, the money is recovered by correcting or appealing the claim, not by balance-billing.
Appeal only when the secondary applied the wrong COB methodology for the plan type — attach both EOBs and the plan's COB provision.
The number 23 is the same reason code in both — what changes is the liability group. OA 23 is Other Adjustment. CO 23 is Contractual Obligation, so the provider absorbs it. Check the prefix on the ERA before you write anything off or bill the patient — a mis-grouped 23 is one of the more winnable appeals.