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CO-P18 Denial Code: Not in Fee Schedule, Comparable Paid

CO-P18 means the procedure you billed isn't listed in the jurisdiction's fee schedule, so the property and casualty payer made an allowance for a comparable service instead. You were paid, but at the rate for the service the payer considered comparable.

Code: CO-P18 (CARC P18)
Status: Active In use since November 1, 2013.
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): The usual group. The difference between your charge and the comparable allowance is the provider's; state rules generally bar billing the claimant.
Official description: Procedure is not listed in the jurisdiction fee schedule. An allowance has been made for a comparable service. To be used for Property and Casualty only.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-P18 means

CARC P18 says procedure is not listed in the jurisdiction fee schedule. An allowance has been made for a comparable service. X12 limits it to property and casualty claims. It replaced deactivated CARC W7.

State workers’ comp and auto fee schedules don’t always list every code. When your code is missing, some payers price it by analogy: they choose a listed code they consider comparable in work and resources, and pay that amount. The remittance reports the difference between your charge and that comparable allowance as CO-P18.

That makes CO-P18 a partial payment, not a denial. The main question is whether the comparison was fair.

Example: you bill a newer procedure code that the state schedule hasn’t adopted. The payer pays at the rate of an older, similar procedure and reports CO-P18. If the new procedure takes substantially more time or resources, the comparable allowance may be too low.

Common causes

New codes not yet added to the state schedule.
Codes deliberately omitted from the schedule.
State schedules based on older code sets or a prior year’s values.
Unusual procedures without a close match in the schedule.

How to check it

Identify the comparable code the payer used.
Compare the work, time, and resources of your service with that code.
Check the state’s rules for pricing unlisted services; some specify a method, such as by-report pricing.
Request reconsideration with the operative or procedure note and a proposed comparable code if the allowance looks low.
Use the state’s fee dispute process within its deadlines if reconsideration fails.

How to prevent problems

Review state fee schedule updates for codes you bill often.
Know each state’s rule for unlisted services before billing.
Attach documentation for new or unusual procedures on P&C bills so payers can price them accurately.

Specialty notes

Surgical specialties and pain management practices performing newer procedures encounter CO-P18 most, since state fee schedules can lag behind national code updates.

Remark codes that may appear with CO-P18

N631 (Medical Fee Schedule does not list this code.): The fee schedule doesn't list this code; an allowance was made for a comparable service.
N657 (This should be billed with the appropriate code for these services.): The service should be billed with the appropriate code.

CO-W7Deactivated (Procedure is not listed in the jurisdiction fee schedule.): The deactivated code that CARC P18 replaced.
CO-P7 (The applicable fee schedule/fee database does not contain the billed code.): The code isn't in the fee schedule, and the payer asks you to rebill rather than paying a comparable code.
CO-P19 (Procedure has a relative value of zero in the jurisdiction fee schedule, therefore no payment is due.): The procedure is listed but has a relative value of zero, so nothing is paid.
CO-P12 (Workers' compensation jurisdictional fee schedule adjustment.): A standard workers' comp fee schedule reduction.

CO-P18 FAQ

What's the difference between CO-P18 and CO-P7?

With CO-P18, the payer picks a comparable listed service and pays it. With CO-P7, the payer denies and asks you to resubmit with a code in the schedule.

How do I know which comparable service was used?

Ask the payer or bill review company. Some remittances or explanations of review name the comparable code; if not, request it in writing.

Can I dispute the comparable allowance?

Yes. If the chosen comparison understates the work, request reconsideration with documentation and a better comparable code, then use the state's fee dispute process if needed.

Does CO-P18 apply to health plans?

No. X12 limits it to property and casualty claims.

Can I bill the claimant the difference after CO-P18?

Usually not. The comparable allowance is treated as the fee schedule amount, and state P&C rules often bar billing the claimant above it.

Important: read before using this information

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