Medicare is a national health insurance plan provided by the government. When you purchase a Medicare Supplement plan (Medigap plan) from a private insurance company, the plans are strictly regulated by the federal and state government. Many people confuse a Medicare Supplement plan ( Medigap plan) with a Medicare Advantage plan. Often people use the term "supplement plan" when they are referring to an "advantage plan". There are major differences between the coverages. If you do not understand those differences, you should really work with an agent who does. There is no cost to using an agent, they get paid by the carrier if you decide to purchase a plan.