Yes, you can keep employer coverage after you turn 65 and enroll in Medicare, but you need to understand how the two plans work together and what happens to your costs.

Many people assume they must drop their employer plan when Medicare starts. That is not true. You can hold both plans at the same time. However, which plan pays first — called the "coordination of benefits" — depends on your employer's size and whether you are still working. The rules are different if you are retired versus still employed, and making the wrong choice can cost you thousands in unexpected bills.

The key decision is whether your employer plan will be your primary insurance (paying first) or whether Medicare will be primary. This affects your deductibles, copays, and which doctors and hospitals you can use. You also need to know that staying on an employer plan may delay or change your Medicare enrollment, and missing certain important date can trigger permanent penalties.

Key Takeaways

  • If you are still working and your employer has 20 or more employees, your employer plan is primary and Medicare is secondary, meaning your employer plan pays first.
  • If you are retired or your employer has fewer than 20 employees, Medicare becomes primary and your employer plan is secondary.
  • You must enroll in Medicare Part A and Part B when you turn 65, even if you keep employer coverage, or you will face late-enrollment penalties that last for life.
  • Staying on an employer plan does not prevent you from joining a Medicare Advantage or Medigap plan, but coordination rules and costs change depending on your situation.
  • You should contact your employer's benefits office and Medicare directly before making changes, because the rules vary by plan and employer size.

How Coordination of Benefits Works When You Have Both Plans

When you have Medicare and an employer plan at the same time, one plan is "primary" and pays its share of your medical bills first. The other plan is "secondary" and pays what is left over, up to its limits. Which plan is primary depends on your work status and your employer's size.

If you are still working and your employer has 20 or more employees, your employer plan is primary. This means your employer plan processes your claim first, applies its deductible and copays, and pays its portion. Medicare then receives the bill and pays what the employer plan did not cover, up to what Medicare would normally pay. You pay any remaining balance.

If you are retired, or if your employer has fewer than 20 employees, Medicare is primary. Medicare processes your claim first and pays its share. Your employer plan then receives the bill and pays what Medicare did not cover, if anything. This usually means lower out-of-pocket costs for you, because Medicare's payment often covers most of the bill and the employer plan covers the gap.

The size threshold of 20 employees applies to your specific employer location or division, not the company as a whole. If you work for a large corporation but your local office has only 15 people, the 20-employee rule does not explore to you.

Medicare Enrollment Rules When You Have Employer Coverage

You must enroll in Medicare Part A and Part B when you turn 65, even if you plan to keep your employer plan. The only exception is if your employer has 20 or more employees and you are still actively working. In that case, you can delay Part B enrollment without penalty as long as you remain employed and covered by the employer plan.

If you miss the important date to enroll in Part B and you do not have this employer coverage exception, you will pay a permanent 10 percent penalty on your Part B premium for every year you were late. This penalty stays with you for life, even after you leave your job. Part A has no penalty if you have employer coverage, but Part B penalties are strict.

To claim the employer coverage exception, you must tell Medicare that you are still working and covered by an employer plan. You do this when you first become may be able to access for Medicare. If you do not report this, Medicare will assume you need to enroll and may automatically sign you up, which can create duplicate coverage and billing confusion.

When you eventually leave your job or lose employer coverage, you have eight months to enroll in Part B without penalty. This is called a "Special Enrollment Period." You must enroll during this window or face the permanent penalty.

What Happens to Your Employer Plan Costs

Your employer plan premiums, deductibles, and copays do not automatically change when you turn 65 and enroll in Medicare. However, some employers reduce their contribution or change the plan design for employees over 65, so your out-of-pocket costs may shift. You should review your employer's benefits summary each year to see if your costs are changing.

Some employers offer a retiree health plan that is separate from the active employee plan. If you retire before 65, you may be moved to this retiree plan, and the rules and costs are often different. When you turn 65, you will need to coordinate this retiree plan with Medicare.

If your employer plan is primary (because you are still working at a company with 20+ employees), you will likely pay less out of pocket than if Medicare were primary, because your employer plan will handle most of the cost. However, you will still pay your employer plan's premiums and cost-sharing, which may be higher than Medicare's.

If your employer plan is secondary (because you are retired or your employer is small), your costs depend on how much the employer plan covers after Medicare pays. Many secondary employer plans cover Medicare's deductibles and copays, which can save you money. Others cover very little. Ask your employer's benefits office what the secondary plan covers.

Choosing Between Employer Coverage and Medicare Advantage or Medigap

You can enroll in a Medicare Advantage plan (Part C) or a Medigap supplemental plan while keeping your employer coverage. However, doing so creates three layers of insurance, and the coordination becomes complex. Most people in this situation stick with their employer plan and Medicare Parts A and B, without adding Advantage or Medigap.

If you are considering dropping your employer plan to join a Medicare Advantage plan, know that you usually cannot re-enroll in your employer plan later. Once you leave, you are off the plan. Some employers allow retirees to rejoin during an annual open enrollment, but this is rare. Check with your benefits office before you make the switch.

If your employer plan is secondary and covers Medicare's gaps well, staying on it is usually cheaper than buying a Medigap plan. Medigap plans have their own premiums, and you would be paying for coverage you already have through your employer. However, if your employer plan is weak or you are worried about losing it when you retire, a Medigap plan gives you portable coverage that does not depend on your job.

Common Mistakes to Avoid

The most common mistake is not enrolling in Medicare Part B on time because you assume your employer plan covers everything. Even if your employer plan is primary, you still need Medicare Part B to avoid the permanent penalty. Many people discover this years later when they retire and try to enroll, only to find they owe back penalties.

Another mistake is not telling Medicare that you have employer coverage. If you do not report the exception, Medicare may automatically enroll you in Part B, creating duplicate coverage and billing problems. Always contact Medicare directly and confirm in writing that your exception has been recorded.

A third mistake is assuming your employer plan will stay the same after you retire. Many employers change or drop retiree coverage, sometimes with little notice. If this happens and you did not enroll in Medigap or Medicare Advantage while you were still covered by the employer plan, you may face higher costs or limited options.

Finally, do not assume you know which plan is primary without checking. The 20-employee rule is often misunderstood, and employer size can change. Contact your employer's benefits office and ask them directly whether your employer plan or Medicare is primary in your situation.

Steps to Take Before Your 65th Birthday

Contact your employer's benefits office at least three months before you turn 65. Ask them: (1) whether your employer has 20 or more employees; (2) whether you can stay on the plan after 65; (3) what your costs will be; and (4) whether you need to do anything to enroll or re-enroll in the plan at 65.

Contact Medicare at 1-800-MEDICARE or visit Medicare.gov. Tell them you are still working and covered by an employer plan. Ask them to note your file so you do not get automatically enrolled in Part B. Confirm in writing that your exception has been recorded.

Review your employer plan's summary of benefits and coverage. Understand your deductible, copays, and which doctors and hospitals are in network. If you are retiring soon, ask whether you will be moved to a retiree plan and what that plan covers.

If you are close to retirement, ask your employer whether they offer retiree health coverage and until what age. If coverage ends at a certain age, plan ahead to enroll in Medigap or Medicare Advantage before that happens.

Frequently Asked Questions

Do I have to enroll in Medicare Part A and Part B if I have employer coverage?

You must enroll in Part A at 65 with no exception. For Part B, you can delay only if you are still working and your employer has 20 or more employees and you are covered by their plan. If you do not meet all three conditions, you must enroll in Part B or face a permanent penalty. Contact Medicare to report your employer coverage exception.

Will my employer plan premiums go up when I turn 65?

Not automatically, but some employers change plan design or contributions for employees over 65. Review your benefits summary each year. If you retire, you may move to a separate retiree plan with different costs. Ask your benefits office what to expect.

Can I drop my employer plan and go back to it later?

Usually no. Once you leave an employer plan, you cannot re-enroll unless the employer offers a special retiree re-enrollment window, which is rare. If you are thinking about dropping it, confirm the re-enrollment policy first.

What if my employer plan is very expensive compared to Medicare Advantage?

You can switch to Medicare Advantage, but you will lose your employer coverage and likely cannot get it back. Before you switch, compare the total cost of the employer plan (premium plus out-of-pocket) to the total cost of Medicare Advantage in your area. Also check whether your doctors are in the Advantage plan's network.

What happens to my employer coverage if I retire before 65?

This depends on your employer's policy. Some offer retiree coverage until 65, some until a later age, and some end coverage when ready. Ask your benefits office what happens at retirement and whether you will be moved to a separate retiree plan. Plan ahead to enroll in Medicare and Medigap or Advantage if your employer coverage ends before 65.