Understanding Medicare: Who Pays First?

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Before diving into the concept of who pays first, let’s briefly explore the fundamental components of Medicare coverage. Medicare is a federal health insurance program primarily designed for individuals aged 65 and older, as well as certain individuals with disabilities. It consists of different parts, each serving specific purposes:

Medicare Part A: Hospital Insurance – Covers inpatient hospital stays, skilled nursing facility care, and some home health and hospice care. b. Medicare Part B: Medical Insurance – Covers doctor visits, outpatient care, medical supplies, and preventive services. c. Medicare Part C: Medicare Advantage – Provides an alternative to Original Medicare (Part A and Part B) by offering comprehensive coverage through private insurance companies approved by Medicare. d. Medicare Part D: Prescription Drug Coverage – Helps pay for prescription medications not covered by Part A or Part B.

Understanding Primary and Secondary Payer Determinations

When you have multiple health insurance plans, such as Medicare and another private insurance, the primary and secondary payer rules come into play. Determining who pays first depends on various factors, including the type of coverage and the coordination of benefits guidelines established by Medicare.

a. Primary Payer: The primary payer is the insurance plan responsible for paying your medical claims first. In most cases, Medicare is the primary payer, but there are exceptions.

b. Secondary Payer: The secondary payer covers costs not paid by the primary payer. If you have other health insurance in addition to Medicare, it typically serves as the secondary payer.

Factors Influencing Primary Payer Determinations

Several factors influence whether Medicare serves as the primary payer or defers to another insurance plan. Here are some key considerations:

a. Employment Status: If you’re still actively working and have health coverage through an employer or union, that plan may be the primary payer until you retire or lose the coverage.

b. Size of Employer: In cases where you have employer group health insurance from a company with 20 or more employees, Medicare usually becomes the secondary payer. If the company has fewer than 20 employees, Medicare becomes the primary payer.

c. End-Stage Renal Disease (ESRD): If you have ESRD and are covered by an employer group health plan, the employer plan generally pays first for the first 30 months of dialysis. After that, Medicare becomes the primary payer.

Coordination of Benefits

To ensure accurate payment and avoid overpayment, coordination of benefits (COB) rules come into play. COB rules outline how multiple insurance plans work together to cover your healthcare expenses. These rules help prevent duplication of payments and protect against fraud.

a. Primary Payer Claim Submission: When you receive healthcare services, submit your claim to the primary payer first, whether it is Medicare or another insurance plan.

b. Explanation of Benefits (EOB): Once the primary payer processes the claim, you will receive an Explanation of Benefits (EOB) statement detailing the covered services and any remaining balance.

c. Secondary Payer Claim Submission: After the primary payer has paid its share, submit the remaining balance to the secondary payer. The secondary payer will then review the claim and make additional payments as necessary.


Understanding who pays first in Medicare can be a complex process, but by familiarizing yourself with the key factors and coordination of benefits guidelines, you can navigate the system more effectively. Remember, it’s essential to stay informed about your specific insurance coverage and consult with your insurance provider or a qualified professional to ensure you receive the maximum benefits from your Medicare plan.


  • Medicare coverage comprises different parts: A, B, C, and D, each serving specific purposes.
  • Primary payer is responsible for paying medical claims first, usually Medicare, while secondary payer covers costs not paid by the primary payer.
  • Factors influencing primary payer determinations include employment status, size of the employer, and End-Stage Renal Disease (ESRD).
  • Coordination of benefits rules ensure accurate payment and avoid duplication of payments between multiple insurance plans.

Useful Links:

  1. Medicare.gov – Coordination of Benefits & Medicare Secondary Payer (TLD: .gov)
  2. Centers for Medicare & Medicaid Services – Medicare Coverage (TLD: .gov)
  3. National Institutes of Health – Medicare Basics (TLD: .gov)
  4. National Council on Aging – Medicare Rights and Resources (TLD: .org)

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