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CO-42 Denial Code (Deactivated): Charge Over Fee Schedule

CO-42 meant the billed charge was higher than the payer's fee schedule or maximum allowable amount, so the excess was reduced. X12 deactivated it and its official text directs payers to use CARC 45 instead.

X12 deactivated CARC42 on June 1, 2007. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals. Use CO-45 instead.

Code: CO-42 (CARC 42)
Status: Deactivated StoppedJune 1, 2007 (in use since January 1, 1995).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): The amount above the fee schedule was a contractual write-off for the provider.
Official description: Charges exceed our fee schedule or maximum allowable amount. (Use CARC 45)
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-42 meant

CARC 42 appeared when your billed charge was more than the payer would recognize for the service. The payer compared the charge to its fee schedule or maximum allowable amount and reduced the line to that figure. The difference between what you billed and what was allowed was reported under code 42.

It was an ordinary pricing adjustment. Most practices set charges above payer rates, so a code like this appeared on nearly every paid claim.

What replaced it

The official description itself says to use CARC 45, so CO-45 is the direct replacement. Code 45 is broader: it also covers contracted and legislated fee arrangements, which is why a separate code 42 was no longer needed.

Two related active codes are worth knowing. CO-131 is for a discount negotiated on a specific claim. CO-P5 covers property and casualty payers that price on reasonable and customary fees.

If you still see CO-42

You will mainly find it in older payment history or in systems with legacy mapping tables. Map it to CARC 45 in your reporting so contractual adjustments are grouped consistently across years.

Handle it the same way you would a CO-45 today: compare the allowed amount to your contracted rate, post the difference as a write-off if it matches, and follow up with the payer if the allowed amount is lower than your agreement.

CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): The direct replacement named in the official text.
CO-131 (Claim specific negotiated discount.): A claim-specific negotiated discount rather than a standard fee schedule cut.
CO-P5 (Based on payer reasonable and customary fees.): Property and casualty reductions based on reasonable and customary fees.

CO-42 FAQ

Is CO-42 the same as CO-45?

In practice yes. X12 retired 42 and pointed payers to 45, which now covers fee schedule, maximum allowable, and contracted or legislated fee arrangements in one code.

Should an old CO-42 be counted as a denial?

No. Like CO-45, it described a pricing reduction, not a rejected claim. Track it with your contractual adjustments.

Important: read before using this information

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