Service not covered per contract
Reviewed by
Robert Thompson, CHBME
Certified Healthcare Business Management Executive
Last reviewed: February 5, 2026
📋 Official X12 Definition
CARC 66: Service not covered per contract. This code is maintained by the X12 organization as part of the External Code List for Claim Adjustment Reason Codes used in electronic healthcare transactions per HIPAA requirements.
💬 What This Means (Plain English)
This service is not covered under the patient's insurance plan. Service not covered per contract according to the plan's benefit design and exclusions.
📖 Detailed Explanation
CARC Code 66 (Service not covered per contract) is part of the standardized code set maintained by X12 and mandated for use in HIPAA-compliant electronic healthcare transactions. This code appears on Explanation of Benefits (EOB) and Electronic Remittance Advice (ERA) documents to explain claim adjustments. This code indicates the service is not a covered benefit under the patient's specific insurance plan. Coverage decisions are based on plan documents, medical policies, and benefit designs that vary widely between plans and payers.
🔍 Common Causes
- Service is explicitly excluded from plan benefits
- Service is considered experimental or investigational
- Service does not meet medical necessity criteria
- Service is cosmetic or not medically necessary per plan
- Benefit maximum or limitation reached for this service type
- Service not covered for this diagnosis or patient age/gender
✅ Step-by-Step Solution
Review Plan Documents
Obtain and review the patient's Summary of Benefits and Coverage (SBC), Certificate of Coverage, or benefit booklet to confirm the exclusion.
Verify Medical Necessity
Review medical records to determine if strong medical necessity exists. Consult with the ordering/performing physician about clinical rationale.
Check for Exceptions
Contact payer to ask if there are any exception processes, such as: compassionate use, experimental/investigational approval pathways, or letter of medical necessity processes.
Appeal with Medical Evidence
If clinically appropriate, file formal appeal with: detailed letter of medical necessity, supporting peer-reviewed literature, clinical guidelines supporting use, treating physician statement, and patient condition documentation.
Explore Alternatives
If appeal is unsuccessful, discuss with provider: alternative covered treatments, manufacturer patient assistance programs, or cash-pay pricing options.
Patient Billing
If all avenues exhausted and service already rendered, bill patient per ABN (Advance Beneficiary Notice) if you had them sign one, or write off if you did not properly notify patient in advance.
📋 Evidence & Documentation Checklist
📞 Insurance Company Call Script
Use these specific questions when contacting the payer:
- I'm calling regarding claim number [CLAIM#] which received adjustment code 66. Can you provide additional details about this adjustment?
- What specific documentation or information would help resolve this issue?
- Is this service specifically excluded from the patient's plan?
- Are there any exceptions or alternative coverage pathways available?
- Is this decision appealable, and what is the appeal process?
- Can you provide a reference number for this call?
- Is there anything else I should know about preventing this issue in the future?
🛡️ Prevention Tips
- Always verify specific service coverage before scheduling
- Obtain Advance Beneficiary Notices (ABNs) for Medicare when appropriate
- Create patient financial responsibility forms for non-covered services
- Maintain database of commonly non-covered services by payer
- Explore prior authorization even when not "required" for borderline services
- Discuss coverage and patient financial responsibility during informed consent
❓ Frequently Asked Questions
What does CARC code 66 mean?
This service is not covered under the patient's insurance plan. Service not covered per contract according to the plan's benefit design and exclusions.
Is CARC 66 appealable?
Yes, CARC code 66 (Service not covered per contract) is appealable. Obtain and review the patient's Summary of Benefits and Coverage (SBC), Certificate of Coverage, or benefit booklet to confirm the exclusion.
How do I fix CARC code 66?
The first step is: Review Plan Documents - Obtain and review the patient's Summary of Benefits and Coverage (SBC), Certificate of Coverage, or benefit booklet to confirm the exclusion.. Then: Verify Medical Necessity - Review medical records to determine if strong medical necessity exists. Consult with the ordering/pe...
What are common causes of CARC 66?
The most common causes include: Service is explicitly excluded from plan benefits; Service is considered experimental or investigational; Service does not meet medical necessity criteria.
Sources & Attribution
- X12 External Code List - CARC (Claim Adjustment Reason Codes) Version 34.0
- CMS Medicare Claims Processing Manual
- HIPAA Transaction and Code Set Standards - 45 CFR Parts 160 and 162
- Washington Publishing Company (WPC) - Official X12 Code List Maintainer
Last Updated: November 1, 2025
Update Cycle: Quarterly (March, July, November)
⚠️ Important Disclaimer
This information is provided for educational purposes only and should not be considered medical, billing, or legal advice. Always verify code interpretations with the specific payer and consult with qualified billing professionals. Code definitions, policies, and payer-specific guidelines may vary and are subject to change without notice. For the most current information, always refer to the latest X12 External Code List and payer-specific policies.