Medicare has four parts, and they cover different things

Part A covers hospital stays, skilled nursing care after a hospital stay, hospice, and some home health services. Part B covers doctor visits, outpatient care, and medical equipment. Part D covers prescription drugs. Part C, also called Medicare Advantage, is an alternative to Parts A and B — it bundles hospital and doctor coverage into one private plan, usually with drug coverage included.

Most people turning 65 are automatically enrolled in Parts A and B. Part D and Part C are optional, but choosing neither one can cost you more later. The differences matter because they determine what you pay out of pocket, which doctors you can see, and whether your prescriptions are covered.

Key Takeaways

  • Part A covers hospital care and skilled nursing; Part B covers doctor visits and outpatient services; most people get both automatically at 65.
  • Part D is prescription drug coverage you must choose during your enrollment window, or you will pay a penalty if you add it later.
  • Part C (Medicare Advantage) replaces Parts A and B with a single private plan that usually includes drug coverage and may offer extra benefits like dental or vision.
  • You cannot have both Original Medicare (Parts A and B) and Medicare Advantage at the same time — you must pick one path.

Part A: Hospital and Skilled Nursing Care

Part A pays for inpatient hospital stays, up to 100 days in a skilled nursing facility after a hospital stay, hospice care, and some home health services. You pay nothing for Part A premiums if you or your spouse paid Medicare taxes for at least 10 years. If you did not, you can buy Part A, but the monthly premium varies.

Part A has a deductible — the amount you pay before Medicare starts paying. For 2024, the Part A deductible is $1,676 per hospital stay. After you meet the deductible, Medicare covers all hospital costs for the first 60 days. Days 61 through 90 require a daily coinsurance amount (a fixed dollar amount per day, not a percentage). Beyond 90 days, you pay the full cost unless you use your "lifetime reserve days," which are limited.

For skilled nursing care, you must have been in a hospital for at least three days first. Medicare covers the first 20 days fully, days 21 through 100 require a daily coinsurance amount, and you pay everything after day 100.

Part B: Doctor Visits and Outpatient Services

Part B covers doctor office visits, preventive care like screenings and vaccines, outpatient surgery, emergency room visits, lab tests, X-rays, and durable medical equipment like wheelchairs or oxygen. Most people pay a monthly premium for Part B — the standard amount for 2024 is $164.90, though it can be higher if your income is above a certain threshold.

Part B also has an annual deductible (currently $240 for 2024). Once you meet it, you typically pay 20 percent of the cost for most services, and Medicare pays 80 percent. For some preventive services — like annual wellness visits, cancer screenings, and flu shots — you pay nothing.

Part B does not cover routine dental, vision, or hearing care. If you need those services, you either pay out of pocket or purchase a separate plan. Some Medicare Advantage plans include dental and vision, which is one reason people choose that route.

Part D: Prescription Drug Coverage

Part D covers prescription medications. You choose a Part D plan from private insurers during your enrollment window. If you do not choose a plan when you first become may be able to access, and you go without drug coverage for more than 63 days, you will owe a late enrollment penalty for as long as you have Medicare — even if you join later.

Part D plans vary widely in cost and which drugs they cover. Each plan has a formulary — a list of covered medications. Some drugs may require prior approval from the plan before the pharmacy will fill them, or they may be covered only at certain pharmacies. You pay a monthly premium, an annual deductible (which varies by plan), and then a percentage of the drug cost or a fixed copay depending on the plan's structure.

If you choose Medicare Advantage (Part C), drug coverage is usually included, so you do not need a separate Part D plan. If you have Original Medicare (Parts A and B), you must choose Part D separately or go without drug coverage.

Part C: Medicare Advantage as an Alternative

Part C, called Medicare Advantage, is a private insurance plan that covers everything Part A and Part B cover, plus usually includes Part D (drug coverage). You do not buy Parts A, B, and D separately — instead, you enroll in one Medicare Advantage plan run by a private company like UnitedHealth, Humana, or Cigna.

Medicare Advantage plans often include benefits Original Medicare does not: dental, vision, hearing, fitness programs, or transportation to medical appointments. However, they usually have a network — you must use doctors and hospitals in that network, or you pay more. Some plans are Health Maintenance Organizations (HMOs), which require you to pick a primary care doctor and get referrals for specialists. Others are Preferred Provider Organizations (PPOs), which give you more flexibility but higher out-of-pocket costs.

The trade-off is that Medicare Advantage plans often have lower monthly premiums than Original Medicare plus a separate Part D plan, but they may have higher deductibles and copays when you use care. You cannot have both Original Medicare and Medicare Advantage at the same time — you must choose one or the other.

How the Parts Work Together

If you choose Original Medicare, you have Part A (hospital) and Part B (doctor) automatically or by choice. You then add Part D (drugs) separately if you want prescription coverage. You may also buy a Medigap plan, which is supplemental insurance that covers some of the costs Medicare does not — like deductibles, coinsurance, and copays.

If you choose Medicare Advantage (Part C), you have one plan that bundles hospital, doctor, and usually drug coverage. You do not buy Medigap with Medicare Advantage — in fact, it is illegal for a Medigap plan to cover you if you have Medicare Advantage.

The choice between Original Medicare and Medicare Advantage depends on your health, your doctors, your budget, and whether you prefer predictable costs (Medigap) or lower premiums (Medicare Advantage). There is no single right answer — it depends on your situation.

Enrollment Windows and Timing

You become may be able to access for Medicare at 65. If you are already receiving Social Security, you are enrolled in Parts A and B automatically. If you are not receiving Social Security, you must sign up during your Initial Enrollment Period, which is the three months before the month you turn 65, the month you turn 65, and the three months after.

If you miss your Initial Enrollment Period, you can enroll during General Enrollment (January 1 through March 31 each year), but you may owe a permanent late enrollment penalty on your Part B premium.

For Part D and Medicare Advantage, there is an annual Open Enrollment Period from October 15 through December 7 each year. You can change plans during this window. If you miss it and do not have drug coverage, you owe the late enrollment penalty.

Frequently Asked Questions

Do I have to take all four parts of Medicare?

No. Part A and Part B are separate decisions (though most people get both). Part D is optional but carries a penalty if you skip it and join later. Part C is an alternative to Parts A and B, not an addition — you choose either Original Medicare or Medicare Advantage, not both.

What is the difference between Original Medicare and Medicare Advantage?

Original Medicare (Parts A and B) lets you see any doctor who accepts Medicare. Medicare Advantage (Part C) is a private plan with a network of doctors and hospitals. Medicare Advantage usually costs less per month but may have higher costs when you use care. Original Medicare usually costs more per month but more predictable costs if you add Medigap.

If I have Medicare Advantage, do I still need Part D?

No. Medicare Advantage plans almost always include prescription drug coverage. You enroll in one plan and get hospital, doctor, and drug coverage together. You do not buy Part D separately.

What happens if I do not choose Part D when I turn 65?

If you go without Part D coverage for more than 63 days, you will owe a late enrollment penalty on top of your Part D premium for as long as you have Medicare. The penalty is about 1 percent of the national average Part D premium per month you were without coverage.

Can I switch from Original Medicare to Medicare Advantage later?

Yes, during the annual Open Enrollment Period (October 15 through December 7). You can also switch from Medicare Advantage back to Original Medicare during this window. Changes take effect January 1 of the following year.