Medicare is primary when you have no other health insurance, and secondary when you do

Primary insurance pays first on your medical bills. Secondary insurance pays what the primary leaves behind. Medicare becomes secondary when you have coverage through an employer, a spouse's employer, TRICARE (military coverage), or a group health plan. The order matters because it changes how much you pay and which insurance company processes your claim first.

The rules differ depending on your age and work status. If you are under 65 and disabled, Medicare is usually secondary to employer coverage. If you are 65 or older and still working, your employer plan is primary if your employer has 20 or more employees. If you are on Medicare and have retiree coverage from a former employer, that plan is usually primary. Understanding which is which prevents claim delays and unexpected bills.

Key Takeaways

  • Medicare is primary only when you have no other health insurance; if you have employer coverage, retiree coverage, or TRICARE, that plan pays first.
  • If you are 65 or older and your current employer has 20 or more employees, your employer plan is primary even though you are on Medicare.
  • When Medicare is secondary, you submit claims to your primary insurance first, and Medicare pays its share of what remains unpaid.
  • You must tell both insurers about each other so they coordinate correctly and do not both deny the same claim.
  • Coordination of benefits rules prevent either insurance from paying more than 100 percent of the bill, which protects you from overpaying.

When your employer plan is primary and Medicare is secondary

If you are 65 or older, still working, and your employer has 20 or more employees, your employer health plan pays first. Medicare pays second. This applies whether you are the employee or the spouse of an employee. The employer plan processes the claim, pays its share, and then sends the remaining balance to Medicare. Medicare then pays what it normally would, up to the amount left unpaid.

You do not need to do anything special to make this work — just make sure both insurers know about each other. When you enroll in Medicare, tell your employer plan that you have Medicare. When you enroll in your employer plan, tell Medicare. If the two insurers do not know about each other, claims can be denied or delayed while they sort out who should pay.

The same rule applies if you have retiree health coverage from a former employer. That coverage is primary, and Medicare is secondary. Retiree plans often coordinate with Medicare automatically because they were designed to work that way, but it is still worth confirming with your plan administrator.

When you are under 65 and disabled

If you are under 65 and receive Medicare because of disability, your employer plan (if you have one) is primary. Medicare is secondary. This is true even if your employer is small. The rule exists because employer plans are assumed to be the main coverage for working-age people, and Medicare fills in the gaps.

If you do not have employer coverage but you have coverage through a spouse's employer, that spouse's plan is primary and Medicare is secondary. If you have both your own employer plan and a spouse's plan, your own plan is primary, the spouse's plan is secondary, and Medicare is third.

When Medicare is primary

Medicare is primary when you have no other health insurance. This is the most common situation for people 65 and older who are retired. If you have only Medicare and a Medigap or Medicare Advantage plan, Medicare is still primary — the supplemental plan is not considered "other insurance" for coordination purposes.

Medicare is also primary if you have TRICARE but are not on active duty. (If you are on active duty, TRICARE is primary.) Medicare is primary if you have coverage through the Veterans Administration, though VA coverage and Medicare work differently and do not coordinate the way employer plans do.

How coordination of benefits works

When you have two insurers, they follow coordination of benefits rules to decide how much each one pays. The primary insurance pays first, up to what it normally would pay. The secondary insurance then looks at what is left unpaid and pays its share of that amount — but not more than it would have paid if it were primary.

Here is a concrete example: your doctor bill is $500. Your employer plan (primary) normally pays 80 percent, so it pays $400. That leaves $100 unpaid. Medicare (secondary) normally pays 80 percent of the allowed amount. If Medicare's allowed amount for that service is $400, it would normally pay $320. But since only $100 is left unpaid, Medicare pays $100 (the smaller amount). You pay $0 instead of the $100 you would have paid if Medicare were primary.

The coordination rules protect you from paying more than you would with either insurance alone. They also prevent either insurance from paying more than 100 percent of the bill. If the primary insurance overpays, the secondary insurance will not pay anything.

What you need to tell each insurance company

When you enroll in Medicare, you will be asked whether you have other health insurance. Answer honestly and provide details: the name of the plan, the group number, and the employer name if it is employer coverage. Medicare uses this information to set itself as secondary in its system.

When you enroll in or renew your employer plan, tell them you have Medicare. Provide your Medicare number. The employer plan needs to know so it can coordinate with Medicare and send claims to Medicare after it processes them. If you do not tell them, the employer plan may process claims as if it is your only insurance, and Medicare may deny claims because it does not know about the employer plan.

If you change jobs or lose employer coverage, update both insurers. If you gain new coverage, tell both your old and new insurers. These updates prevent claim problems and may support the right insurance pays in the right order.

What happens if the insurers do not coordinate

If your insurers do not know about each other, both may deny the same claim or both may pay, leaving you to sort out the mess. The primary insurance may deny because it thinks Medicare should pay. Medicare may deny because it thinks the other insurance should pay. You end up calling both companies and providing proof that you have both coverages.

To avoid this, keep copies of your insurance cards for both plans. When you submit a claim, include both insurance information. If a claim is denied, ask the insurance company why — the denial letter will tell you whether they think another insurance should pay. Then contact the other insurance and provide proof of the denial.

Some providers will submit claims to both insurers automatically if you give them both card numbers at the time of service. Ask your doctor's office or hospital whether they do this. If they do, you still need to make sure both insurers know about each other, but the provider handles the submission order.

Frequently Asked Questions

If I am 65 and still working, do I have to take Medicare right away?

No. If your employer has 20 or more employees, you can delay Medicare enrollment without penalty as long as you stay on your employer plan. Once you leave that job or lose the coverage, you have a limited time to enroll in Medicare without paying a late penalty. Talk to your employer's benefits office about the timing that works for your situation.

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

The primary insurance always pays first, regardless of disagreement. If there is a dispute about which is primary, federal law sets the order: employer plans with 20+ employees are primary for people 65+, and employer plans are primary for people under 65 with disability. You can ask your employer's benefits office or Medicare to clarify, but the law does not change based on what either company thinks.

Do I need a Medigap plan if I have employer coverage?

Not necessarily. Employer plans and retiree plans often cover more than Medicare alone, so you may not need a Medigap supplement. Compare what your employer plan covers against what Medicare covers, and what you would pay out of pocket under each. Some people keep both; others drop Medigap when they have good employer coverage.

If I have Medicare and TRICARE, which pays first?

TRICARE pays first if you are on active duty. If you are retired from the military or a family member of someone on active duty, Medicare is primary and TRICARE is secondary. The order depends on your military status, so check your TRICARE documentation or call TRICARE to confirm.

What if I have Medicare and coverage through my spouse's employer?

Your spouse's employer plan is primary, and your Medicare is secondary. You do not need to be the employee yourself — coverage as a spouse counts. Make sure both the employer plan and Medicare know about each other so claims coordinate correctly.