Medicare is primary when you are 65 or older with no other group health coverage

Primary insurance is the one that pays your medical bills first. Secondary insurance pays what the primary leaves behind. For most people 65 and older, Medicare is primary — it gets the first look at your bills and pays its share before any other insurance does anything.

But there are situations where Medicare is not primary. If you are still working and your employer offers health coverage, your employer plan is primary and Medicare is secondary. If you are under 65 and have Medicare because of disability or end-stage renal disease, group health coverage from your job or a family member's job is primary. If you have both Medicare and Medicaid, Medicaid is usually secondary, but in some cases Medicaid pays first for certain services.

Knowing which insurance is primary matters because it changes what you pay out of pocket and which insurance company handles the claim first. The primary insurance always processes the claim and decides what it will cover. The secondary insurance then sees what was paid and covers additional costs — or sometimes nothing at all.

Key Takeaways

  • Medicare is primary for most people 65 and older who do not have group health coverage through an employer or spouse's employer.
  • If you are still working and your employer offers health insurance, your employer plan is primary and Medicare is secondary, even after age 65.
  • If you are under 65 with Medicare due to disability or kidney disease, your employer group plan is primary and Medicare is secondary.
  • When Medicare is secondary, you must tell the provider and your employer plan about both insurances so claims route correctly.
  • Coordination of benefits rules prevent both insurances from paying the full amount, so you may still owe a portion of the bill.

When you are 65 or older and Medicare is primary

If you are 65 or older and you do not have group health insurance through an employer, Medicare is your primary insurance. This includes people who are retired, self-employed without a group plan, or covered only by a spouse's retiree health plan that is not active group coverage.

When Medicare is primary, you submit claims to Medicare first. Medicare reviews the claim, applies your deductible and coinsurance, and pays its portion. Any remaining balance goes to your secondary insurance (if you have one) or becomes your responsibility. This is the standard situation for most seniors.

If you have a Medigap policy (also called supplemental insurance), it works as your secondary. Medigap is designed to cover costs that Medicare does not — copayments, coinsurance, and sometimes the Part B deductible. When Medicare is primary and you have Medigap, the coordination usually works smoothly because Medigap policies are built around Medicare's payment structure.

When you are still working and your employer plan is primary

If you are 65 or older but still working, and your employer offers health coverage, your employer plan is primary and Medicare is secondary — even though you are old enough for Medicare. This applies whether you work full-time or part-time, as long as the employer has 20 or more employees. The rule is the same if you are covered as a spouse on an active employee's plan.

This means your employer plan gets the first look at your medical bills. It processes the claim and pays according to its rules. Medicare then sees what your employer plan paid and covers additional costs up to what Medicare would have paid on its own. You coordinate between two insurances, which can be confusing, but it protects your employer plan from paying more than it should.

You must tell your healthcare providers that you have both employer coverage and Medicare, and that the employer plan is primary. If you do not, claims may route to Medicare first, and Medicare will deny them because it knows you have group coverage. This delays payment and can create billing problems.

When you are under 65 with Medicare and your employer plan is primary

If you are under 65 and have Medicare because of disability or end-stage renal disease, your employer group health plan is primary if you are still working or covered as a dependent on someone else's active employee plan. Medicare is secondary in this situation, even though you are the one with the Medicare card.

The employer plan processes your claim first and pays according to its coverage rules. Medicare then reviews what the employer plan paid and covers additional costs. This coordination protects your employer plan from paying more than Medicare would have paid, and it means you may have lower out-of-pocket costs because two insurances are sharing the bill.

As with working seniors, you must inform your providers that your employer plan is primary. If you do not, Medicare may receive the claim first and deny it, knowing that you have group coverage available. Always list both insurances on your registration forms and tell the billing department which one is primary.

How coordination of benefits works when you have two insurances

When you have both Medicare and another insurance, the two plans coordinate their payments so that neither one pays more than 100 percent of the bill. This is called coordination of benefits. The primary insurance pays first, and the secondary insurance pays only what is left over — and only up to what it would have paid if it were primary.

Here is a concrete example: suppose you have a medical bill for $500. Your employer plan is primary and pays $350 (its standard coinsurance). Medicare is secondary. Medicare would normally pay $400 on the same bill. But because the employer plan already paid $350, Medicare pays only $50 more, bringing the total to $400. You owe the remaining $100. Neither insurance pays more than it would have on its own, and you do not get a windfall from having two plans.

The secondary insurance never pays before seeing what the primary paid. This is why it is critical to tell providers which insurance is primary — if the claim goes to the wrong insurance first, it delays the whole process and can create billing errors that take months to untangle.

Medicare and Medicaid coordination

If you have both Medicare and Medicaid, the coordination depends on which state you live in and what services you need. In most cases, Medicare is primary and Medicaid is secondary. Medicare processes your claim first, and Medicaid covers costs that Medicare does not pay — such as your Part B deductible or coinsurance — up to what Medicaid allows.

However, for certain services like long-term care or prescription drugs, Medicaid may pay first or have different rules. Some states have programs that help pay your Medicare premiums and cost-sharing if your income is low. The rules vary by state, so you should contact your state Medicaid office or a local aging services agency to understand how your specific coverage works.

If you are unsure whether you have Medicaid, check your mail for a Medicaid card or contact your state's Medicaid program directly. Do not assume you are covered just because you applied or were told you might be. Medicaid coverage must be active for it to coordinate with Medicare.

What to tell your doctor and insurance company

When you see a healthcare provider, always bring both insurance cards and tell the office staff which insurance is primary. Write it down on your registration form: "Primary: [Insurance Name]" and "Secondary: [Insurance Name]." This prevents the office from sending the claim to the wrong insurance first.

If your primary insurance changes — for example, you retire and lose your employer coverage — notify your providers and your secondary insurance right away. Medicare has a system to track primary and secondary coverage, but it relies on accurate information from you and your employers. If the information is wrong, claims may be denied or delayed.

Keep copies of your insurance cards, policy numbers, and group numbers in a safe place. When you call your insurance company with a question, have this information ready. If you are coordinating between Medicare and another plan, write down the name of the person you spoke with, the date, and what they told you. This creates a record if there is a billing dispute later.

When to contact Medicare or your other insurance

Contact Medicare if you receive a bill you think Medicare should have paid, or if you are unsure whether Medicare is your primary or secondary insurance. You can call Medicare at 1-800-MEDICARE (1-800-633-4227) or visit Medicare.gov. Have your Medicare number ready.

Contact your employer plan or other insurance if you receive a bill from them and do not understand why they denied it or paid less than you expected. Ask them to explain which insurance they believe is primary and to show you the coordination of benefits calculation. If they made an error, ask them to reprocess the claim.

If you have a dispute between two insurances about who should pay, contact your state's insurance commissioner's office. They have a department that handles complaints about coordination of benefits and can investigate if one insurance is not following the rules.

Frequently Asked Questions

Can I choose which insurance is primary if I have both Medicare and employer coverage?

No. The rules about which insurance is primary are set by federal law, not by your choice. If you are 65 or older and still working for an employer with 20 or more employees, your employer plan must be primary. You cannot ask Medicare to be primary instead. However, you can choose whether to enroll in your employer plan — if you decline it, Medicare becomes primary.

What happens if I do not tell my provider which insurance is primary?

The claim may go to the wrong insurance first, which will deny it because it knows you have other coverage. This delays payment and creates extra work for the provider's billing department. Eventually the claim routes to the correct primary insurance, but it can take weeks. Always inform providers of both insurances and which one is primary.

If Medicare is secondary, do I still pay my Medicare premiums?

Yes. You pay your Medicare Part B and Part D premiums regardless of whether Medicare is primary or secondary. Your employer plan does not replace Medicare premiums. However, if your income is very low, you may be able to get help paying Medicare premiums through your state's Medicaid program or a Medicare Savings Account program.

Does my Medigap policy work the same way if Medicare is secondary?

No. Medigap policies are designed to work when Medicare is primary. If Medicare is secondary (because you have employer coverage), your Medigap policy may not cover much, or it may not work at all. Some people who are still working keep their Medigap policy but it sits unused until they retire. Check with your Medigap insurance company about how your policy coordinates when Medicare is secondary.

What if my employer plan and Medicare disagree about who should pay?

Contact both insurances and ask them to review the coordination of benefits rules. If they still disagree, file a complaint with your state's insurance commissioner. You can also ask your healthcare provider's billing department to help resolve the dispute — they deal with coordination issues regularly and may be able to clarify which insurance should have paid.