When you have Medicare and another form of health insurance, coordination of benefits rules determine which plan pays first (primary) and which pays second (secondary). The primary payer processes the claim first and pays its share. The secondary payer then covers some or all of the remaining balance.
Medicare Primary vs. Secondary: Quick Reference
| Your Situation | Medicare Pays | Other Insurance Pays |
|---|---|---|
Medicare is your only coverage | Primary | N/A |
You have employer coverage, employer has 20+ employees, you are actively working | Secondary | Primary |
You have employer coverage, employer has fewer than 20 employees | Primary | Secondary |
You are retired with retiree insurance | Primary | Secondary |
You have COBRA | Primary | Secondary |
You have a Medigap (Medicare Supplement) plan | Primary | Secondary (Medigap fills gaps) |
You have Medicaid | Primary | Secondary (Medicaid pays last) |
You have VA benefits | Each pays separately for its own services | Each pays separately |
You have workers' compensation for a work-related injury | Secondary | Primary (workers' comp pays first) |
You have TRICARE (military retiree) | Primary | Secondary |
Employer Size Matters for Active Workers
If you are still working and your employer has 20 or more employees, your employer plan is primary and Medicare is secondary. If your employer has fewer than 20 employees, Medicare is primary. Enrolling in Part B is especially important in the smaller-employer scenario, as your employer plan may pay very little without Medicare as the primary payer.
What Happens If a Claim Is Filed Out of Order?
If a claim is submitted to the secondary payer first, it will typically be denied or returned with a request for the primary payer's explanation of benefits (EOB). Always submit claims to the primary payer first. If you are unsure which plan is primary, call the Benefits Coordination and Recovery Center (BCRC) at 1-855-798-2627.
Does Medicare Advantage change the coordination of benefits rules?
No. If you have Medicare Advantage, the same coordination of benefits rules apply. Your Medicare Advantage plan acts in place of Original Medicare and coordinates with other coverage using the same primary/secondary framework.
If Medicare is secondary, do I still need to enroll in Part B?
Yes, in most cases. Even if Medicare is secondary, you need to be enrolled in Part B for it to pay as a secondary payer. Failing to enroll in Part B can leave you with uncovered costs.
How does Medigap work with coordination of benefits?
Medigap always pays after Original Medicare. Medicare pays first as primary, then Medigap covers some or all of the remaining cost-sharing (deductibles, coinsurance, copayments) depending on your plan.
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