Original Medicare is the government plan you join at 65: Part A for hospital stays, Part B for doctors and outpatient care. It pays most of a bill but not all of it, and — the part that surprises people — it has no yearly limit on what you can end up owing.
That gap is why almost nobody keeps it alone, and it leaves two ways forward.
Medigap (also called a supplement) is a private policy you buy alongside Original Medicare to pay the share it leaves behind. You keep any doctor in the country who takes Medicare, and you pay a monthly premium for the supplement — plus a separate drug plan, called Part D.
Medicare Advantage is the other way: one private plan replaces the lot, usually including drugs and often dental, frequently for little or no extra premium. In exchange you use the plan’s network of doctors, may need referrals, and it has its own yearly out-of-pocket limit.
Not sure which suits you? The Medicare Path Chooser ranks them against your doctors, health and travel — this calculator prices whichever you pick.