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CO-102 Denial Code: Major Medical Adjustment

CO-102 is a major medical adjustment. The payer adjusted the claim because part of it was processed under the plan's major medical benefit rather than its base benefit, changing the allowed or paid amount. The payer's remittance and plan terms explain the calculation.

Quick facts

Code
CO-102 (CARC 102)
Status
Active In use since January 1, 1995.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The adjustment is treated as a contractual or plan-calculation difference the provider does not collect from the patient.
  • PR (Patient Responsibility): Some payers report a major medical difference as patient responsibility when the major medical benefit carries its own cost-sharing.
Official description
Major Medical Adjustment.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-102 means

CARC 102 reads major medical adjustment. It comes from plan designs where coverage has two layers: a basic benefit that pays first for certain services, and a major medical benefit that picks up covered expenses beyond the basic layer, usually with its own deductible and coinsurance. When part of a claim moves from one layer to the other, the payer reports the resulting difference as CARC 102.

The code is uncommon today because most plans use a single comprehensive benefit. When it does appear, it is usually from an older plan design, a supplemental plan, or an administrator that still separates the two layers in its system.

The adjustment itself is not a rejection of the service. It explains why the allowed or paid amount differs from what the base benefit alone would produce.

Common causes

  • The base benefit was exhausted for the period, and the rest of the claim was processed under major medical.
  • The service is covered only under the major medical layer, which applies different allowances.
  • Major medical cost-sharing was applied separately from the base plan’s cost-sharing.
  • The payer’s system calculated the layers differently from what you expected based on the eligibility response.

How to fix it

  1. Read the full remittance. Look for accompanying deductible or coinsurance adjustments and any remark codes that describe the calculation.
  2. Call the payer if the math is unclear. Ask which portion was paid under the base benefit, which under major medical, and why.
  3. Post the adjustment per group code. Under CO it is a provider adjustment; under PR, move it to the patient’s balance.
  4. Request reprocessing if the payer applied the wrong layer, for example because benefits had not actually been exhausted. Follow the payer’s reconsideration process.
  5. No corrected claim is needed unless the payer tells you claim data drove the error.

How to prevent problems with CO-102

  • During eligibility checks, ask whether the plan has separate basic and major medical benefits and note remaining balances for each.
  • Tell patients with layered plans that their share may change once the base benefit is used up.
  • Map CARC 102 in your practice management system so it is not lumped in with denials.
  • If you see it often from one administrator, ask for a written explanation of how it applies the layers. Our guide on reading CARC and RARC codes covers how to separate adjustments from denials.
  • PR-1 / PR-2 (Deductible and coinsurance amounts.): Standard patient cost-sharing, which X12 once split into separate major medical deductible and coinsurance codes before deactivating them.
  • CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): The usual fee schedule or contracted-rate reduction.
  • PR-119 (Benefit maximum for this time period or occurrence has been reached.): Benefit maximum for the period reached, which can shift processing between benefit layers.
  • OA-23 (The impact of prior payer(s) adjudication including payments and/or adjustments. (Use only with Group Code OA)): Impact of a prior payer's adjudication, common where a base plan and a second plan both apply.

CO-102 FAQ

What is a major medical plan?

Historically, some coverage was built in layers: a base plan paying certain services first, with a major medical layer covering larger or remaining expenses with its own deductible and coinsurance. Some plans still use that structure.

Is CO-102 a denial?

No. It is a calculation adjustment explaining how the payer applied the major medical layer. The claim was processed.

How do I check a CO-102 amount?

Ask the payer to explain how the base and major medical benefits were applied, then compare the result with the plan summary and your contract.