Medicare: Eligibility, the Four Parts, and Enrollment Windows
Domain 1 tests the machinery behind every sale: what Medicare is, who qualifies, how the parts fit together, and when a beneficiary is allowed to enroll. Expect scenario items that turn on a date, a penalty, or which part pays for a given service.
The four parts
- Part A (hospital insurance) covers inpatient hospital stays, skilled nursing facility care after a qualifying inpatient stay, hospice, and some home health. Most beneficiaries get it premium-free with 40 quarters of Medicare-covered work; others may buy in.
- Part B (medical insurance) covers physician services, outpatient care, durable medical equipment, labs, and preventive services. It carries a monthly premium, generally 20% coinsurance with no annual out-of-pocket cap, and income-related premium adjustments (IRMAA) based on modified adjusted gross income from two years earlier.
- Part C is Medicare Advantage: private plans that deliver Part A and Part B benefits, and usually Part D.
- Part D is outpatient prescription drug coverage, sold as a standalone PDP or bundled into an MA-PD plan.
Who qualifies
Age 65 with citizenship or five years of lawful permanent residency; under 65 after 24 months of Social Security disability benefits; or at any age with ALS, or with ESRD under separate rules.
The Initial Enrollment Period
The IEP is seven months long: the three months before the birthday month, the birthday month, and the three months after. Enrolling in the last three months can delay the effective date. A beneficiary still working with creditable employer coverage may delay Part B without penalty, but must enroll within eight months of losing that coverage.
Worked example
A member turns 65 in July, keeps working, and stays on her employer group plan. She does not enroll in Part B now. When she retires two years later she has an eight-month Special Enrollment Period, and because the group coverage was creditable, no late penalty applies. Had she moved to COBRA instead, that SEP would not be available.
Traps that cost marks
Confusing the General Enrollment Period (January 1–March 31) with the fall Annual Enrollment Period; assuming the 20% Part B coinsurance has a cap; and treating the Part B late penalty as a one-time charge when it is 10% per 12-month period, for life.