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N357 Remark Code: Time Frame Between Services Not Met

N357 means the payer requires a certain amount of time between this service, procedure, or supply and a related one, and that requirement was not met. The service was billed too soon, or too late, relative to the related service.

Code: N357 (RARC N357)
Status: Active In use since November 18, 2005.
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): The service was denied for failing the payer's timing rule. The provider absorbs it unless the timing was reported wrong or an exception applies.
PR (Patient Responsibility): Where the patient chose to receive the service early after being told it might not be covered, some plans allow the amount to shift to the patient.
Official description: Time frame requirements between this service/procedure/supply and a related service/procedure/supply have not been met.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What N357 means

Many services come with spacing rules. A replacement supply may only be payable after a set interval, a follow-up procedure may need to occur within a certain window after the first, or a repeat test may not be covered again until a period has passed. N357 is the payer’s signal that the required interval between your service and a related one was not satisfied.

It often appears with CARC 119 or CARC 151, and with CARC B15 when the issue is that a prerequisite service didn’t come first.

Common causes

A supply or item was refilled or replaced before the payer’s minimum interval.
A repeat test was done sooner than the policy allows, often by a different provider.
The prior service date in the payer’s history is wrong, or belongs to a different patient.
A date-of-service error placed your service inside the restricted window.
Clinical circumstances justified the earlier service, but the claim didn’t include the modifier or documentation the payer accepts for exceptions.

What to do

Ask the payer, or check its portal, for the date and code of the related service it matched against.
Compare that date with your service date and the payer’s policy interval.
If a date is wrong on your claim, correct it and resubmit as a corrected claim (frequency code 7).
If an exception applies, such as a change in condition or loss of an item, appeal with records showing why the service was needed sooner.
If the rule was simply not met, write off or bill the patient according to plan rules and any advance notice you obtained.

How to prevent it

Check the patient’s recent service history before dispensing or scheduling interval-limited services. Where your system allows it, store each payer’s intervals so staff see a warning when a service is due too soon.

Codes that may appear with N357

PR-119 (Benefit maximum for this time period or occurrence has been reached.): The benefit maximum for the time period has been reached.
CO-151 (Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.): The information does not support this frequency of services.
CO-B15 (This service/procedure requires that a qualifying service/procedure be received and covered.): A required qualifying service was not received first, when the timing rule is about sequence.

M86 (Service denied because payment already made for same/similar procedure within set time frame.): Says payment was already made for the same or a similar procedure within a set time frame.
N118 (This service is not paid if billed more than once every 28 days.): An example of a specific timing rule: not paid if billed more than once every 28 days.
N435 (Exceeds number/frequency approved /allowed within time period without support documentation.): Used when the number or frequency allowed within a period is exceeded without supporting documentation.

N357 FAQ

What kinds of services have time frame rules?

Replacement supplies, repeat tests, follow-up procedures, some drugs, and equipment are common examples. Each payer sets its own intervals.

Can I wait and rebill later?

Not for the same date of service. You can provide the service again once the interval has passed, but the original date will still fail the rule.

What if the earlier service was billed by someone else?

The payer still counts it. Ask the payer for the date and provider of the related service so you can confirm the timing.

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