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N123 Remark Code: Split Service, Partial Units

N123 is an alert that the payer split the original service line. The line carrying N123 represents only a portion of the units that were originally submitted; the rest of the units appear on another line, often with a different outcome.

Quick facts

Code
N123 (RARC N123)
Status
Active In use since September 24, 2002; last modified March 1, 2016.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): If the split portion is denied or reduced, the adjustment is typically the provider's under the payer's unit rules.
  • OA (Other Adjustment): Some payers use an other adjustment to show the split without assigning liability on that portion.
Official description
Alert: This is a split service and represents a portion of the units from the originally submitted service.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N123 means

You billed one line with several units. The payer’s remittance now shows two or more lines for that charge. N123 marks a line created by that split: its unit count is only part of what you sent.

The alert itself asks for no action. What matters is the reason code on each piece, which tells you why the units were handled differently.

What to do

  1. Group the split lines together by date of service and procedure so the full charge can be reconciled.
  2. Read the reason codes on each portion. Paid units may show routine adjustments, while denied units usually carry a frequency, authorization, or maximum-units reason.
  3. Act on the denied portion if needed: correct units, obtain retro authorization, or appeal with documentation.
  4. Check your posting software so it does not treat the split portion as an unmatched or duplicate line.

Unit limits and how payers enforce them are covered in the units of service guide.

Codes that may appear with N123

  • 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 many services, a common reason some units are split off and denied.
  • PR-119 (Benefit maximum for this time period or occurrence has been reached.): A benefit maximum was reached, so units beyond it were split off.
  • N362 (The number of Days or Units of Service exceeds our acceptable maximum.): The number of days or units exceeds the acceptable maximum.
  • N640 (Exceeds number/frequency approved/allowed within time period.): Exceeds the number or frequency approved or allowed within a time period.

N123 FAQ

Why did the payer split my line?

Usually because some units met its rules and others did not, such as units beyond an authorization or a daily maximum. Splitting lets it pay the eligible units and adjust the rest.

How should I post a split line?

Add the units and amounts across all lines that came from the original charge, and confirm they total what you billed.

Should I appeal the denied portion?

Only if you have documentation supporting the extra units. Address the reason code on the denied portion, not N123 itself.