CO P18 denial code

Claim adjustment reason code P18. Often reported as CO P18.

Priced like a similar service

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What P18 means

Your code was not in the jurisdiction's fee schedule, so the carrier borrowed the price of a service it judged similar.

Expect it from workers' compensation or auto medical carriers, since it is limited to property and casualty claims. The payer could not find the code in the applicable fee schedule but did not deny it. Instead it priced it based on a service it considers comparable.

Whether the comparison is fair is the question to check, since the allowance depends entirely on which service the payer chose.

Group codes seen with P18

On a remittance, P18 comes after a group code. These are the ones it is most often reported with:

• CO P18 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The procedure is not in the current jurisdictional fee schedule.
• An unlisted or new code was billed.
• The payer's comparable service was priced lower than the billed service.

What to do next

1. Find out which comparable service the payer used for pricing.
2. Request reconsideration if a better comparison exists, with support.
3. Post the remaining balance as an adjustment if the pricing is acceptable.

Related codes

• P7 (reason code) Code not in the fee schedule or database
• P9 (reason code) No matching CPT or HCPCS code
• P19 (reason code) Zero relative value in fee schedule