How does Medicare Supplement insurance work?

If you buy a Medicare Supplement insurance policy, you will pay a monthly premium to the private Medicare Supplement insurance company that sells you the policy. Keep in mind, this may be on top of the deductibles you are paying for Medicare Part A and Part B. You must be enrolled in both Part A and Part B to purchase a Medigap policy.
If you are in Original Medicare (Parts A and B) and you have a Medigap policy, first Medicare pays its share of the Medicare-approved amounts for your covered health care costs. Then your Medigap policy pays its share of the cost. Any remaining costs would be your responsibility.