Part B Medical Billing 2026 – Claims, Coverage Rules & Denial Prevention

Medicare Part B reimburses outpatient physician services, preventive visits, certain procedures, and durable medical equipment. For most practices, Part B claims represent the largest portion of Medicare revenue, so accuracy directly affects cash flow.

Billing under Part B is complex. CPT and HCPCS codes, modifiers, and documentation requirements change yearly, and small errors, like incorrect E/M coding, missing modifiers, or improper service reporting, can result in claim denials, audits, or recoupments.

Understanding the specific coverage rules, coding nuances, and documentation requirements is essential to maintain compliance and ensure timely reimbursement.

What Is Medicare Part B?

Medicare Part B is the outpatient portion of Original Medicare. While Part A covers inpatient hospital stays, skilled nursing, and hospice, Part B covers:

• Physician and non-physician practitioner (NPP) services
• Outpatient hospital services
• Preventive care and screenings
• Durable medical equipment (DME)
• Laboratory and diagnostic tests
• Mental health services
• Ambulance services
• Home health services (when not covered by Part A)

How Part B Reimbursement Works

Part B medical billing reimbursement is based on the Medicare Physician Fee Schedule (MPFS). Every covered service is assigned a set of Relative Value Units (RVUs) composed of:

• Work RVU: reflects provider time, skill, and mental effort
• Practice Expense RVU: covers overhead costs
• Malpractice RVU: accounts for professional liability insurance costs

These are then multiplied by a Conversion Factor (CF), a dollar amount updated annually by CMS. For 2024, CMS set the conversion factor at $32.74 per RVU, a reduction from the 2023 rate.

Medicare pays 80% of the Medicare-approved amount after the patient’s annual deductible ($240 for 2024). The remaining 20% is the patient’s coinsurance responsibility.

Part B Claim Submission: The CMS-1500 Form

All Part B professional services are billed on the CMS-1500 claim form (or its electronic equivalent, the 837P transaction). Key fields include:

• Box 21: ICD-10-CM diagnosis codes (up to 12)
• Box 24B: Place of Service code
• Box 24D: CPT/HCPCS procedure code with modifiers
• Box 24E: Diagnosis pointer (links each service to the relevant diagnosis)
• Box 24F: Charges
• Box 24J: Rendering provider NPI
• Box 33: Billing provider information (Group NPI)

Part B Medical Billing: Coverage and Timely Filing Rules

Medicare Part B reimburses outpatient physician services, preventive care, procedures, and durable medical equipment. Claims must be filed within 12 months of the service date; late submissions are denied, and providers cannot bill patients.

Claims are processed by 12 Medicare Administrative Contractors (MACs) across the U.S. Submitting to the wrong MAC or missing deadlines can delay payment or trigger denials.

Preventive visits, screenings, and procedures often require specific CPT/HCPCS codes and documentation, and some services may need prior authorization. Tracking MAC updates, confirming coverage rules, and submitting on time are essential to avoid denials and ensure accurate reimbursement.

Key Covered Services Under Part B Medical Billing

Medicare Part B covers outpatient physician visits, preventive care, behavioral health, procedures, durable medical equipment, labs, and telehealth. Accurate coding is essential for proper reimbursement, as each service type has its own rules, documentation requirements, and modifiers. Timely filing with the correct MAC jurisdiction ensures claims are processed without delays or denials.

The Advance Beneficiary Notice (ABN) in Part B Billing

When a service may not be covered by Medicare Part B, providers are required to issue an Advance Beneficiary Notice of Noncoverage (ABN). This notice protects both the patient and the provider: without a valid ABN, you cannot collect payment from the patient if Medicare denies the claim.

A proper ABN must include:

• Service-specific details: clearly identify which service may not be covered.
• Reason for possible denial: explain why Medicare might not pay, such as experimental treatment or non-covered procedure.
• Estimated cost: give the patient a realistic range of out-of-pocket expenses.
• Patient acknowledgment: the patient must sign the ABN before the service is provided.

For billing, when a non-covered service is performed with a valid ABN, you must append modifier GA to the claim line. This modifier signals to Medicare that the patient has been informed and accepted financial responsibility. Proper use of ABNs helps prevent denials, compliance issues, and patient disputes, making it an essential part of Part B billing workflows.

Part B Medical Billing: Incident-To Rules

Incident-to-billing allows a Medicare-enrolled physician to bill for services performed by a non-physician practitioner (NPP), such as a nurse practitioner (NP), physician assistant (PA), or licensed clinical social worker (LCSW), under the physician’s NPI. This means the service is reimbursed at 100% of the Medicare Part B rate, instead of the 85% rate typically paid to NPPs.

To qualify for incident-to billing, the service must meet all of the following criteria:

• Be a follow-up visit for a condition previously initiated by the supervising physician.
• Take place in the physician’s office or clinic (POS 11).
• Have the physician immediately available on-site to assist if needed; availability by phone alone does not qualify.
• Occur within an established plan of care created and signed by the supervising physician.

It is important to note that new patients or new medical problems do not qualify for incident-to billing. In those cases, the NPP must bill under their own NPI at the standard 85% Medicare rate. Proper adherence to incident-to rules ensures maximum reimbursement while maintaining compliance with CMS guidelines.

Common Part B Billing Denials and Solutions

Even experienced providers encounter claim denials under Medicare Part B. Understanding the common reasons and how to fix them can prevent lost revenue and reduce compliance risk.

• CO-4: Incorrect Modifier
  Issue: The claim line has the wrong modifier.
  Solution: Verify the modifier requirements according to the payer’s Local Coverage Determinations (LCDs) before submitting.
• CO-97: Bundling
  Issue: Services were incorrectly bundled under NCCI edits.
  Solution: Review NCCI edits and bill unbundled services using modifier 59 when allowed.
• CO-50: Non-Covered Service
  Issue: Medicare determines the service is not covered.
  Solution: Issue a valid ABN and append modifier GX or GA to indicate the patient accepted financial responsibility.
• PR-96: Not Covered by Plan
  Issue: The service is excluded under the patient’s specific plan.
  Solution: Bill secondary insurance if available and collect any patient balance as needed.
• CO-167: Diagnosis Not Covered
  Issue: The ICD-10 code does not support medical necessity for the billed service.
  Solution: Review the LCD and ensure the ICD-10 diagnosis accurately reflects medical necessity.

Many denials can be prevented by pre-checking claims against LCDs, coding manuals, and payer rules, and by ensuring documentation supports every service billed.

Maximize Your Medicare Part B Revenue with Expert Billing Support

Part B billing is complex and financially critical. From RVU-based reimbursement to ABNs, incident-to rules, and timely filing, every detail matters. Mistakes directly impact revenue and compliance.

At Delaware Medical Billing, our specialists stay current with every CMS update and MAC bulletin. We manage your claims end-to-end, submission, denial management, and appeals, so you can focus on patient care while maximizing revenue.

Schedule your Free Consultation Today and stop leaving Medicare reimbursement on the table.

Frequently Asked Questions

1. What is the difference between Medicare Part B and Medicare Advantage for billing purposes?

Traditional Medicare Part B uses CMS fee schedules and MACs for processing. Medicare Advantage (Part C) plans are offered by private insurers who must cover at a minimum what traditional Medicare covers. Still, they may use different billing portals, prior authorization requirements, and reimbursement rates. Always verify payer-specific rules for MA plans, even when using Medicare codes.

2. Can a provider who opts out of Medicare still get paid through Part B?

A provider who opts out of Medicare cannot receive Part B reimbursement. Patients can still see opted-out providers but must sign a private contract agreeing to pay out of pocket. Medicare will not reimburse patients for opted-out provider services except in emergencies.

3. How does sequestration affect Part B payments?

Under the Budget Control Act and ongoing continuing resolutions, Medicare payments are subject to sequestration, a mandatory across-the-board reduction. As of 2024, sequestration reduces Part B payments by 2%. This applies after all other adjustments, including the conversion factor.

4. What are the MPPR rules in Part B billing?

The Multiple Procedure Payment Reduction (MPPR) applies when a provider performs multiple imaging or therapy services on the same day. CMS reduces payment on the second and subsequent procedures. In therapy, the practice expense component is reduced by 50% for procedures beyond the first.

5. What is a Local Coverage Determination (LCD) and how does it affect Part B claims?

A MAC issues an LCD to define Medicare coverage for a specific service in its jurisdiction. If your claim doesn’t include a diagnosis code listed in the applicable LCD, it may be denied for lack of medical necessity. Always check the relevant LCD before submitting claims for high-risk services.