What Is Medicare? A Guide to Parts A, B, C and D

Medicare is federal health insurance. Most people become eligible around age 65; some qualify earlier because of disability, end-stage renal disease (ESRD) or ALS.

Part A mainly covers hospital care; Part B generally covers doctors and outpatient services; Part C is Medicare Advantage from private insurers; and Part D covers prescription drugs.

1. Who May Qualify?

Eligibility may arise at age 65 with qualifying citizenship or lawful residence, or through certain disabilities, ESRD or ALS. Eligibility does not make every part free. Premiums and enrollment depend on work history, current coverage and income.

Some people receiving Social Security or Railroad Retirement benefits are enrolled automatically; others must apply. Check ahead rather than assuming automatic enrollment.

2. Part A: Hospital Insurance

Part A generally helps with inpatient hospital care, eligible skilled nursing, hospice and some home health services. It is not long-term care insurance and generally does not pay for long-term custodial help with bathing, dressing or eating.

Most people owe no Part A premium based on their own or a spouse's Medicare-tax work history. For 2026, those without premium-free Part A generally pay $311 or $565 monthly; the inpatient hospital deductible is $1,736 per benefit period.

3. Part B: Doctors and Outpatient Care

Part B generally helps pay for doctors, outpatient care, preventive services, tests, imaging, qualifying ambulance services, durable medical equipment and some outpatient drugs.

For 2026, the standard Part B premium is $202.90 monthly and the annual deductible is $283. After the deductible, Original Medicare generally pays 80% of the Medicare-approved amount for many covered services, and you pay 20%. Higher-income beneficiaries may owe IRMAA.

4. Part C: Medicare Advantage

Medicare Advantage is an alternative way to receive Parts A and B through a Medicare-approved private plan. You still have Medicare and generally continue paying the Part B premium. Most plans include Part D; some offer dental, vision, hearing, fitness or over-the-counter benefits. Networks, referrals, prior authorization, copays and service-area rules may apply.

5. Part D: Prescription Drugs

Part D helps pay for outpatient prescriptions. Original Medicare beneficiaries may buy a stand-alone plan; most Medicare Advantage plans include drug coverage. Each plan's formulary, tiers, pharmacies, deductible and authorization rules differ. Compare the exact medication, dose, frequency and pharmacy.

6. Two Main Coverage Paths

Original Medicare combines Parts A and B and generally permits use of providers nationwide that accept Medicare; you may add Part D and Medigap. Original Medicare itself has no annual medical out-of-pocket maximum.

Medicare Advantage administers Parts A and B and usually includes Part D. It has an annual out-of-pocket limit for covered Part A and B services, but network and plan rules may apply.

7. What Does Original Medicare Usually Not Cover?

Most routine dental, routine vision and eyeglasses, hearing aids, long-term custodial care, routine care outside the United States, massage, cosmetic surgery and private-duty nursing are generally not covered. Specific medical circumstances can create exceptions.

8. When Should You Enroll?

The initial enrollment period is generally seven months: the three months before your 65th birthday month, the birthday month and the following three months. Some people with coverage from current employment through themselves or a spouse can delay Part B, but employer size and current-employment status matter.

COBRA and retiree coverage generally are not equivalent to current-employment coverage. Medicare enrollment generally stops eligibility to contribute to an HSA; premium-free Part A may have retroactive effective dates for delayed applicants.

9. What If You Miss a Deadline?

General enrollment generally runs January 1 through March 31. Certain coverage loss, moves or other events may create a special enrollment period with event-specific deadlines. Part B penalties generally increase the premium by 10% for each full 12-month delay. A Part D penalty may apply after 63 consecutive days without Part D or other creditable drug coverage.

10. A Practical Checklist

Confirm Part A and B effective dates and whether you must apply. List doctors, hospitals, prescriptions and pharmacies; compare Original Medicare with Part D and Medigap against Medicare Advantage; and check coordination with employer coverage, Medicaid, Medicare Savings Programs or Extra Help. Review plans annually rather than copying a friend's choice.

Key takeaway: Medicare does not cover everything. Confirm eligibility and timing first, then compare plans using your providers, prescriptions, budget and travel needs.

This is general education, not legal, tax, medical or individual insurance advice. Dollar amounts above are for 2026 and can change in later years. Verify current eligibility, costs and coverage with Medicare and plan documents.