A Medicare supplement, or Medigap policy cannot be used to pay Medicare Advantage copays or deductibles. Medicare supplement insurance works only with original Medicare. Therefore, if you have a Medicare supplement policy and decide to switch to a Medicare Advantage plan (also called Medicare Part C) you should contact the Medicare supplement carrier and drop that plan.

If you have a Medicare Advantage plan it is illegal for an agent to sell you a Medicare supplement. If anyone tries to do that, you should contact your state insurance regulator.

During a person’s original open enrollment period it is possible to choose either original Medicare and a Medicare supplement or a Medicare Advantage plan. The Medicare Advantage plan may include Part D prescription drug coverage, or a separate Part D plan can be selected. However there are different initial open enrollment periods for different plans. The original open enrollment period for Medicare Advantage and Part D prescription drug plans lasts for 7 months. It covers the three months before one’s 65th birthday, the birthday month, and three months after the birthday month. The original open enrollment period for Medicare supplement plans begins the month of one’s 65th birthday and lasts 6 months. During open enrollment, any Medicare plan can be selected on a guaranteed issues basis; one cannot be turned down due to health issues.

After the original open enrollment period, switching between original Medicare and Medicare Advantage, or vice versa, can be a little more complicated.

Medicare Advantage and Medicare Part D have an annual open enrollment period from October 15 through December 7. During that time one can change to or from a Medicare Advantage plan; switch from one Medicare Advantage plan to another; and join, drop or switch Part D plans.

In addition, one can leave a Medicare Advantage plan during a disenrollment period, returning to original Medicare, between January 1 and February 14. If one leaves a Medicare Advantage plan he or she has until February 14 to enroll in a Part D prescription drug plan.

There is no time limit on purchasing a Medicare supplement policy, but it will most likely not be available on a guaranteed issue basis unless it is purchased during an open enrollment period. The insurance company can consider pre-existing conditions and may charge a higher premium, require a waiting period for coverage, or deny coverage. There is an exception if one leaves original Medicare to join a Medicare Advantage plan but wants to return to original Medicare within 12 months. In that case, one may be able to get back the same Medicare supplement he or she had before, provided the company still sells it. If one joined the Medicare Advantage plan when he or she was first eligible and leaves that plan to return to original Medicare within 12 months, he or she can purchase any Medicare supplement policy

There are special open enrollment period is some other cases. For example, if an insurance company goes out of business, or stops offering a Medicare Advantage plan or Medicare supplement plan, those people who lose coverage as a result will most likely be able to join another plan or purchase other insurance on a guaranteed issue basis. Similarly, if one was covered by an employer provided insurance plan and lost coverage either because employment ends or the employer changes plans, then he or she will have a special open enrollment period.