Medicare information verified for 2026Plain-English Medicare education
Medicare learning center

Understanding the Four Parts of Medicare

Learn what Parts A, B, C, and D cover and how they may work together for your healthcare needs.

Who is eligible for Medicare?

Most people first become eligible at 65. Medicare can also begin earlier after certain periods of disability or for people with specific medical conditions. Eligibility does not always mean you should enroll in every part immediately—active employer coverage can change the timing.

Your seven-month Initial Enrollment Period generally begins three months before the month you turn 65, includes your birthday month, and ends three months afterward.

The parts of Medicare

AHospitalInpatient care, skilled nursing, hospice
BMedicalDoctors, outpatient care, equipment
CAdvantageA private-plan way to receive A + B
DPrescriptionsOutpatient drug coverage

Part A · Hospital insurance

Part A helps cover inpatient hospital care, skilled nursing facility care after a qualifying stay, hospice, and certain home health services. Most beneficiaries do not pay a monthly Part A premium because they or a spouse earned enough work credits.

Part B · Medical insurance

Part B helps cover physician services, outpatient care, preventive services, durable medical equipment, and other medically necessary services. It normally has a monthly premium, an annual deductible, and coinsurance.

Part C · Medicare Advantage

Part C is another way to receive Part A and Part B benefits through a private Medicare-approved insurer. Many plans include Part D and additional benefits. Networks, prior authorization, copays, and service areas can apply.

Part D · Prescription drug coverage

Part D is outpatient prescription drug coverage offered by private Medicare-approved plans. Formularies, preferred pharmacies, premiums, and cost sharing vary by plan and can change each calendar year.

What Original Medicare does not fully cover

  • Original Medicare has no annual out-of-pocket maximum.
  • Routine dental, routine vision, and hearing aids are generally not covered.
  • Most long-term custodial care is not covered.
  • Prescription drugs taken at home generally require Part D coverage.
  • Foreign travel coverage is limited.
HSA warning: Once Medicare begins, you can no longer contribute to an HSA. Part A can sometimes be retroactive, so coordinate the stop date before applying.

Enrollment periods to know

Period Timing What it is for
Initial Enrollment 7 months around age 65 Your first opportunity to enroll in Medicare
Annual Election Oct. 15–Dec. 7 Changes to Medicare Advantage and Part D for the next year
Medicare Advantage Open Enrollment Jan. 1–Mar. 31 One change for people already enrolled in Medicare Advantage
General Enrollment Jan. 1–Mar. 31 Part A/Part B enrollment when another period is unavailable
Special Enrollment Depends on event Enrollment after qualifying coverage or life events