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N523 Remark Code: Outlier Payment Limit Reached

N523 means the payer has a limit on outlier payments for a service period, that limit has been met, and the outlier payment that would otherwise apply to this claim was not paid. The base payment may still be made; only the outlier add-on is withheld.

Code: N523 (RARC N523)
Status: Active In use since March 1, 2010.
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): The unpaid outlier amount is a payment limitation under the payer's rules. It is not billable to the patient.
Official description: The limitation on outlier payments defined by this payer for this service period has been met. The outlier payment otherwise applicable to this claim has not been paid.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What N523 means

Prospective payment systems pay a set amount per stay or episode. For unusually expensive cases, many add an outlier payment on top. Some payers also cap how much in outlier payments a provider, or a program as a whole, can receive during a defined period.

N523 tells you that cap was hit. The claim qualified for, or would have been evaluated for, an outlier payment, but because the limit for the service period is already met, that portion was not paid. The rest of the claim is processed normally.

This remark is aimed mainly at institutional and home health providers paid under prospective systems.

Why it happens

The provider received substantial outlier payments earlier in the period.
The payer’s cap is calculated as a share of total payments, and outlier claims were a large part of the provider’s volume.
Claims for the period were processed in an order that placed this claim after the cap was reached.

What to do

Confirm the rule. Ask the payer, or check program guidance, which cap applies and how it is measured.
Verify the numbers. Compare the payer’s outlier total for the period with your own records.
Request correction if the payer applied the cap to the wrong period or included claims that did not belong.
Post the unpaid outlier amount as a contractual adjustment once confirmed.
Report it internally, since it affects margin forecasting for high-cost cases.

How to plan for it

Track outlier payments against the cap throughout the period. Finance teams that know when they are near a cap can anticipate the revenue effect rather than finding it on the remittance.

Codes that may appear with N523

CO-70 (Cost outlier - Adjustment to compensate for additional costs.): Cost outlier: the type of additional payment that N523 says was not made.
CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): Some payers report the reduction as a fee schedule or maximum allowable adjustment.
CO-223 (Adjustment code for mandated federal, state or local law/regulation that is not already covered by another code and is mandated before a new code…): Used by some payers when the limit comes from a mandated law or regulation.

CO-69 (Day outlier amount.): Day outlier amount, a different outlier type.
N444 (Alert: This facility has not filed the Election for High Cost Outlier form with the Division of Workers' Compensation.): A workers' compensation facility has not filed a required high cost outlier election.
N130 (Consult plan benefit documents/guidelines for information about restrictions for this service.): Points to plan or program documents for the payment limitation.

N523 FAQ

What is an outlier payment?

It is an additional payment for unusually costly cases that exceed the normal prospective payment, such as a very expensive inpatient stay or home health episode.

Who uses outlier caps?

Caps are set by the payer or program. Medicare's home health outlier cap, which limits each agency's outlier payments to a share of its total payments, is one well-known example.

Can I appeal N523?

You can ask the payer to confirm the cap and the calculation. If the payer applied the wrong period or miscounted prior outlier payments, request correction.

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