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N415 Remark Code: Allowed Once in 18 Months

N415 means this service is allowed one time in an 18-month period. The payer found the same service already allowed within the previous 18 months, so this claim line was denied or reduced as exceeding the frequency limit.

Quick facts

Code
N415 (RARC N415)
Status
Active In use since August 1, 2007; last modified July 1, 2016.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The service was billed before the 18-month interval passed and the payer applied the limit under contract terms. Write the amount off unless your contract says otherwise.
  • PR (Patient Responsibility): The patient's benefit covers only one service per 18 months, so the patient may owe the balance with proper advance notice.
Official description
This service is allowed 1 time in an 18-month period.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N415 means

N415 enforces an 18-month interval. The plan pays for the service once, then expects 18 months to pass before paying for it again. If the payer’s history shows an allowed service within that period, the new line fails. N415 usually sits beside CARC 119 or CARC 151 on the remittance.

Why long intervals cause denials

Short limits are easy to remember. An 18-month window is not. By the time a patient returns, staff may have changed, records may have moved systems, or the patient may simply not remember when the last service happened. Specific triggers include:

  • The prior service happened more than a year ago, so it felt “due,” but it was still inside 18 months.
  • The earlier service was performed at another location that billed the same payer.
  • The earlier claim was dated incorrectly, making the interval look shorter than it was.
  • A replacement or repeat was needed early due to a clinical change, and the claim did not explain it.

What to do

  1. Find the earlier date of service the payer used and check it against the record.
  2. Do the math. Using the payer’s counting method, confirm whether the new date really falls inside 18 months.
  3. Fix data problems first. A wrong date on either claim should be corrected; for the current claim, send a corrected claim with resubmission code 7.
  4. Explain early need. If a change in the patient’s condition justified repeating the service sooner, appeal or request an exception with documentation.
  5. Otherwise accept the adjustment, and bill the patient only if your contract and prior notice allow it.

How to prevent it

Store the last date of service for long-interval items where schedulers can see it. Set the recall or reorder date to land after the 18-month mark, not at the one-year point. When a patient reports the service was done elsewhere, record that date too.

Codes that may appear with N415

  • PR-119 (Benefit maximum for this time period or occurrence has been reached.): The benefit maximum for the period was reached; N415 sets that period at 18 months.
  • CO-151 (Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.): The payer does not consider this frequency supported by the information submitted.
  • N411 (This service is allowed one time in a 6-month period.): A shorter interval: once every six months.
  • N416 (This service is allowed 1 time in a 3-year period.): A longer interval: once every three years.
  • N117 (This service is paid only once in a patient's lifetime.): The strictest version: a service payable only once in a lifetime.

N415 FAQ

Why would a plan use 18 months instead of a year or two?

It is a plan design choice. Payers set intervals based on how often they consider a service or item reasonable. The reason does not change the rule, so verify it against the plan documents.

Does a prior service under a different plan count?

Usually only services the same payer allowed are in its history. If the patient had the service under a previous insurer, this payer may not know about it, but it may still ask.

How do I figure out the earliest payable date?

Take the date of the last allowed service and add 18 months using the payer's counting method. Ask the payer to confirm if you are close to the boundary.