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N12 Remark Code: Member Not in Required Medicare Part

N12 means the policy is a Medicare supplement, but the member does not appear to be enrolled in the applicable part of Medicare. The member is responsible for the portion of the charge Medicare would have covered.

Code: N12 (RARC N12)
Status: Active In use since January 1, 2000; last modified August 1, 2007.
Code set: Remittance Advice Remark Codes (RARC)
Group codes: PR (Patient Responsibility): The amount Medicare would have paid is assigned to the patient because the supplemental policy will not pick up Medicare's share.
OA (Other Adjustment): Some payers report the Medicare-equivalent portion as another adjustment. Treat it as a coverage-gap issue, not a provider write-off, until Medicare enrollment is confirmed.
Official description: Policy provides coverage supplemental to Medicare. As the member does not appear to be enrolled in the applicable part of Medicare, the member is responsible for payment of the portion of the charge that would have been covered by Medicare.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What N12 means

A Medicare supplement (Medigap-type) policy is designed to pay after Medicare, covering gaps such as deductibles and coinsurance. It is not built to replace Medicare’s own payment. When the supplement’s records show the member is not enrolled in the Medicare part that would normally cover the service, such as Part B for physician services, the supplement pays only its share and leaves Medicare’s portion with the patient. N12 is how it explains that split.

The accompanying CARC varies by payer; non-covered (CARC 96), coordination of benefits (CARC 22), and eligibility codes such as CARC 177 all fit the situation.

Common causes

The patient dropped or delayed Medicare Part B enrollment but kept the supplement.
Medicare coverage ended and the supplement’s records reflect that.
The claim went straight to the supplement without being billed to Medicare first, and the payer could not find active Medicare coverage.
The supplement’s enrollment data is stale or has a mismatched Medicare ID.

What to do

Check Medicare eligibility for the date of service using the patient’s Medicare ID.
If Medicare is active, submit the claim to Medicare. Then let the crossover reach the supplement, or bill the supplement with Medicare’s remittance, and ask it to reprocess.
If Medicare is not active, explain to the patient that they owe the Medicare-equivalent portion and bill according to the remittance.
Ask the patient to contact the supplement if its records are wrong, so future claims process correctly.

How to prevent it

Verify Medicare Part A and Part B status at registration for every patient who presents a supplement card, and bill Medicare first. See eligibility and COB root causes for a broader checklist.

Codes that may appear with N12

CO-96 (Non-covered charge(s).): Non-covered charge; N12 explains that the charge is outside the supplement because Medicare should have been primary.
OA-22 (This care may be covered by another payer per coordination of benefits.): Coordination of benefits points to Medicare as the payer that should process first.
CO-177 (Patient has not met the required eligibility requirements.): The patient has not met an eligibility requirement, here enrollment in the relevant Medicare part.

N6 (Under FEHB law (U.S.C. 8904(b)), we cannot pay more for covered care than the amount Medicare would have allowed if the patient were enrolled in…): FEHB plans limiting payment to what Medicare would have allowed for members without Medicare.
MA04 (Secondary payment cannot be considered without the identity of or payment information from the primary payer.): Secondary payment cannot be considered without the primary payer's identity or payment data.
N193 (Alert: Specific federal/state/local program may cover this service through another payer.): Alert that another federal, state, or local program may cover the service.

N12 FAQ

What if the patient actually has Medicare?

Bill Medicare first with the correct Medicare ID. Once Medicare pays, the supplement can process its share from the crossover or your secondary claim.

Can I bill the patient for the whole charge?

N12 says the member owes the part Medicare would have covered. The supplement may still owe its own share, so read the full remittance before sending a patient statement.

Why would someone have a Medigap policy without Medicare?

Enrollment can lapse, a Part B enrollment may have been delayed, or the payer's records may be out of date. Confirm current status before assuming the patient is uninsured for that part.

Important: read before using this information

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