Original Medicare: Parts A & B

Part A helps cover inpatient hospital stays, skilled nursing care after a qualifying stay, hospice, and some home health care. Most people pay no monthly premium for Part A, because they (or a spouse) paid Medicare taxes while working.

Premium-free does not mean cost-free: Part A has a deductible per benefit period and coinsurance for longer stays, which is a large part of why most people add more coverage on top of Original Medicare.

Part B helps cover doctor visits, outpatient care, preventive services, lab work, and durable medical equipment. It carries a monthly premium set each year — higher-income households pay an income-adjusted amount (IRMAA), based on the tax return from two years earlier.

After an annual deductible, Part B generally pays 80% of approved charges. The remaining 20% has no annual cap under Original Medicare alone — the single most important fact in the whole system, and the reason the Supplement-vs-Advantage decision exists.

Original Medicare generally does not cover prescription drugs you take at home (that is Part D), routine dental, vision, or hearing care, or long-term custodial care. Each gap has its own solution — and its own deadline.