The four parts, quickly

Part A covers hospital stays. Part B covers doctor visits and outpatient care. Part C (Medicare Advantage) bundles A and B — often with extras — through a private insurer. Part D covers prescription drugs.

Advantage vs. Supplement

Medicare Advantage plans usually have lower premiums and added benefits (dental, vision), but use a network — similar to an HMO or PPO.

Medicare Supplement (Medigap) plans cost more monthly but let you see any doctor who accepts Medicare, with fewer surprise bills. You’ll typically pair it with a separate Part D plan.

Enrollment windows that matter

Initial Enrollment Period: the 7-month window around your 65th birthday. Missing it can mean permanent late penalties.

Annual Enrollment Period (Oct 15 – Dec 7): the yearly window to switch plans for the following year.

Medicare Advantage Open Enrollment (Jan 1 – Mar 31): a second chance to switch Advantage plans or move back to Original Medicare.

Common mistakes

Assuming your current doctors are in-network without checking. Not comparing Part D drug formularies against your actual prescriptions. Waiting past your Initial Enrollment Period, which can trigger permanent premium penalties.