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N631 Remark Code: Priced as a Comparable Service

N631 means the medical fee schedule the payer uses does not list the code you billed, so the payer made an allowance based on a comparable service instead. The payment reflects the value of that substitute code.

Quick facts

Code
N631 (RARC N631)
Status
Active In use since July 15, 2013.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The difference between your charge and the comparable-service allowance is a provider adjustment.
Official description
Medical Fee Schedule does not list this code. An allowance was made for a comparable service.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N631 means

Workers’ compensation and other jurisdictional fee schedules list maximum fees by code. When your code isn’t on the list, the payer has to decide how to price it. N631 says it did this by choosing a comparable listed service and paying based on that code’s value.

It closely matches CARC P18 and can appear with CARC 45. It is different from CARC P7, where the payer asks you to resubmit with a code it recognizes.

Why codes are missing

  • New codes haven’t been added to the jurisdiction’s fee schedule yet.
  • The fee schedule is based on an older code set for the date of service.
  • The service is unlisted or by report.
  • The jurisdiction excludes the code on purpose.

What to do

  1. Ask which comparable code the payer used.
  2. Check whether it’s reasonable. Compare the work, time, and resources of the two services.
  3. Review the fee schedule’s ground rules for unlisted and unvalued services. Some require a report or invoice and allow negotiation.
  4. Request reconsideration with documentation if the comparison undervalues your service.
  5. Post the adjustment if you agree.

How to prevent surprises

When billing workers’ comp or auto for newer codes, check the jurisdiction’s current fee schedule first. If the code isn’t listed, send supporting documentation with the bill so the payer can pick an appropriate comparison. An ERA analysis can show which codes repeatedly get priced this way.

Codes that may appear with N631

  • CO-P18 (Procedure is not listed in the jurisdiction fee schedule.): The procedure isn't in the jurisdiction fee schedule; an allowance was made for a comparable service.
  • CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): The charge exceeds the fee schedule or maximum allowable amount.
  • CO-P7 (The applicable fee schedule/fee database does not contain the billed code.): The fee schedule doesn't contain the billed code; resubmit with an appropriate code.
  • N449 (Payment based on a comparable drug/service/supply.): Payment based on a comparable drug, service, or supply.
  • N448 (This drug/service/supply is not included in the fee schedule or contracted/legislated fee arrangement.): The service isn't included in the fee schedule or contracted fee arrangement.

N631 FAQ

Which comparable service did the payer use?

N631 doesn't say. Ask the payer or adjuster which code it used and why, so you can check the allowance.

Why would a valid code be missing from the fee schedule?

State fee schedules are updated on their own timelines and may not include new codes, or may purposely exclude some. Unlisted and by-report services are also common.

Should I change the code I billed?

Bill the code that accurately describes the service. If the fee schedule requires a specific substitute, follow its rules.