A Medicare Supplement (a.k.a Medigap) plan is an insurance policy that assists, or supplements the benefits in Original Medicare Part’s A and B. It doesn’t have anything to do with Medicare Advantage or your Part D prescription coverage — it only works with Original Medicare Part’s A and B.
As I mentioned in the article that compared Original Medicare and Medicare Advantage, there is some cost-sharing in Original Medicare in the form of deductibles, co-pays and coinsurance. The job of the Medigap plan is to eliminate some, or all of that cost-sharing.
It’s also important to understand what Medigap plans don’t cover. In general, they don’t cover dental, hearing, or vision, and they don’t cover prescription drugs either however in some cases Part B and your Medigap will cover drugs related to serious diseases like cancer and/or H.I.V..
Similar to Advantage plans, some (but not many) Medigap plans also offer a health club reimbursement feature.
Medigap plans revolve around Medicare Part B meaning that when you take Part B you should also enroll in the Medigap plan at that time (unless you have other coverage like group employer coverage, retiree coverage, TriCare, or Medicaid)