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N351 Remark Code: Service Outside Treatment Plan Dates

N351 means the service was provided on a date outside the start and end dates of the treatment plan the payer approved, so it was not covered under that plan.

Quick facts

Code
N351 (RARC N351)
Status
Active In use since August 1, 2005.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The service fell outside the approved dates, so the provider absorbs the adjustment unless it can obtain an extension or win an appeal.
  • PR (Patient Responsibility): Some payers assign the amount to the patient if the patient agreed in advance to pay for care outside the approved plan. Check the payer's rules first.
Official description
Service date outside of the approved treatment plan service dates.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N351 means

When a payer approves a course of treatment, it approves it for a period. Visits inside that window are eligible for payment; visits before it starts or after it ends are not. N351 says your date of service fell outside the approved plan dates.

N351 often accompanies CARC 198 (authorization exceeded) or CARC 197 (authorization absent), and sometimes CARC 272 when the payer frames it as a program rule.

Common causes

  • The plan expired and visits continued while a renewal request was pending or never sent.
  • Treatment started before the approval’s start date, for example on the evaluation day.
  • The payer approved different dates than the provider requested, and the schedule was not updated.
  • A date-of-service typo placed an otherwise valid visit outside the window.
  • The patient paused care, and the resumed visits fell after the end date.

What to do

  1. Pull the approval. Confirm the exact start and end dates and any visit limits.
  2. Check the service date. If it was keyed wrong, correct it and submit a corrected claim (frequency code 7).
  3. Request an extension if the payer permits retroactive approval, and include the clinical notes that justify continued care.
  4. Appeal when you have evidence the plan was approved for those dates or the payer’s record is wrong.
  5. Review patient liability. Only bill the patient if the payer’s rules and your notices allow it.

For a wider look at approvals and their windows, see authorization and referral denials.

How to prevent it

Track each plan’s end date and visit count next to the patient’s schedule and trigger a renewal request well before the plan ends. Block scheduling beyond the approved dates unless a renewal is pending, and confirm new approval dates as soon as they arrive.

Codes that may appear with N351

  • CO-198 (Precertification/notification/authorization/pre-treatment exceeded.): Precertification or authorization was exceeded, as when visits continue after the plan's end date.
  • CO-197 (Precertification/authorization/notification/pre-treatment absent.): Precertification or authorization is absent for the dates billed.
  • CO-272 (Coverage/program guidelines were not met.): Coverage or program guidelines were not met.
  • N54 (Claim information is inconsistent with pre-certified/authorized services.): States the claim is inconsistent with pre-certified or authorized services.
  • N238 (Incomplete/invalid physician certified plan of care.): Used when the physician-certified plan of care is incomplete or invalid.
  • N322 (Missing/incomplete/invalid last certification date.): Covers a missing or invalid last certification date.

N351 FAQ

What is an approved treatment plan?

It is a plan of care, often for therapy, behavioral health, home health, or dental work, that the payer has reviewed and approved for a set date range and sometimes a set number of visits.

Can the treatment plan dates be extended after the fact?

Some payers allow a retroactive extension or late authorization in limited circumstances. Many do not, so request extensions before the current plan ends.

Is N351 the same as an authorization denial?

It is closely related. The service may have been authorized in principle, but the date of service falls outside the window the approval covers.