En español | Many people with Medicare also have health coverage from elsewhere. How this works depends on the type of coverage you have:

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Group health insurance from a current employer

Most employers cannot require employees (or their spouses) who turn 65 to sign up for Medicare. While still working, you must be offered the same benefit options as younger employees. If you do sign up for Medicare and your employer has fewer than 20 workers (or fewer than 100 if you have Medicare through disability), then Medicare becomes primary. This means Medicare pays your medical claims first and your employer plan serves as secondary insurance, covering services that Medicare doesn't, according to the plan's terms.

Retiree health benefits

Medicare Parts A and B are always primary to retiree coverage provided by a former employer or union. In effect, your plan becomes supplemental insurance that improves on Medicare — maybe covering some services that Medicare doesn't, or paying some of Medicare's out-of-pocket costs. Contact your retiree plan to find out exactly how it fits in with Medicare. If the plan provides "creditable" drug coverage — meaning that Medicare considers it at least as good as Part D coverage — you don't need Part D. Your retiree plan's administrators can tell you whether it's creditable or not.

Federal retiree health benefits

If you're covered by the federal employee health benefits program, you are not required to join Medicare Part B when you retire. But if you later wanted to enroll — perhaps if your plan became too expensive to keep up — you'd then get a late penalty. If you keep your plan and join Medicare, then Medicare becomes primary, as explained above, and you can switch to a lower-cost federal health plan for secondary coverage if you want to. If your plan provides creditable drug coverage, you don't need Part D. (For more information on FEHP benefits and Medicare, see the Office of Personnel Management's guide to frequently asked questions. )

Veterans health benefits

With coverage from Veterans Affairs, you're not required to enroll in Part B, but the VA recommends it. Medicare increases coverage beyond VA hospitals and doctors – which could be important if you had to be taken to a non-VA facility in an emergency. You can use your VA card at VA facilities and your Medicare card elsewhere. Also, delaying enrollment could result in a Part B late penalty if you lose VA benefits or want to enroll in Medicare in the future.

While in the VA program, you don't need Part D. If you lose drug coverage, you won't receive a late penalty if you enroll in a Part D drug plan within two months. Part D might be worth having if you qualify for Extra Help. (See the VA's guidance for veterans eligible for Medicare.)

Military retiree health benefits

While still on active duty, you and your covered spouse continue to receive TriCare benefits, even if either of you is older than 65. But if you're retired, you're switched from TriCare to the TriCare for Life (TFL) program at age 65, and so is your covered spouse when he or she reaches 65. You must then enroll in Medicare Part A and Part B, which become primary, and TFL serves as supplemental insurance. If you don't enroll, TFL cannot pay for any services that Medicare covers. This rule also applies if you're retired and you or your spouse becomes eligible for Medicare at an earlier age due to disability. In the TFL program, there is no premium to pay but you must pay the Medicare Part B premium. You don't need Part D. (For more information, see the military's guidance on TFL and Medicare.)

Coordination of benefits

Be sure to fill out a form you receive from Medicare asking you to specify other coverage. Your benefits can then be coordinated automatically without your having to file paperwork for claims. For more information on how Medicare works with other insurance (including liability insurance), see the publication "Medicare and Other Health Benefits: Your Guide to Who Pays First" (PDF). In complicated situations, call the Medicare Coordination of Benefits contractor at 1-800-999-1118. 

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