Medicare Supplement plans, also called “Medigap” plans, are private insurance plans that help fill “gaps” in Original Medicare. Original Medicare pays for much of your covered health care services and supplies, but you are responsible for some out-of-pocket costs. Medicare Supplement policies help reduce your out-of-pocket costs by paying some of the expenses not covered by Original Medicare. Medicare Supplement policies are not Medicare Advantage plans and work very differently than Medicare Advantage plans. They do not replace Original Medicare Parts A and B, like Medicare Advantage but coordinates with Original Medicare.