Medicare has four separate parts, and each covers different services

Medicare Part A covers hospital stays, skilled nursing care after a hospital stay, hospice care, and some home health services. Medicare Part B covers doctor visits, outpatient care, medical equipment, and preventive services. Medicare Part D covers prescription drugs. Medicare Advantage (Part C) is an alternative to Parts A and B — it is a single plan run by a private insurance company that must cover everything Part A and B cover, but often includes Part D and other services as well.

Most people who turn 65 are automatically enrolled in Part A and Part B. Part D and Part C are optional, and you choose whether to add them. Understanding what each part does helps you know what costs you are responsible for and what services are covered when you need care.

Key Takeaways

  • Part A covers hospital and skilled nursing stays; Part B covers doctor visits and outpatient services; Part D covers prescription drugs; and Part C (Advantage) is a private alternative that bundles A and B coverage.
  • You are automatically enrolled in Part A and Part B at 65 if you are receiving Social Security, but you must actively choose Part D or Part C.
  • Each part has different costs: Part A has a deductible per hospital stay, Part B has a monthly premium and deductible, and Part D premiums vary by plan.
  • If you choose Part C (Advantage), you do not pay Part A and B premiums separately, but you use the Advantage plan's network of doctors and hospitals instead.
  • You can switch between Original Medicare (A and B) and Advantage plans during the annual enrollment period in the fall, but missing the important date means waiting until the next year.

Medicare Part A: Hospital and Skilled Nursing Care

Part A covers inpatient hospital stays, which means you are admitted to the hospital overnight. It pays for your room, meals, nursing care, and most hospital services while you are there. You pay a deductible for each hospital stay — the amount changes each year, but it is the same whether you stay one night or thirty nights. After you pay the deductible, Medicare covers all costs for days 1 through 60. Days 61 through 90 require a daily copayment from you. Beyond 90 days, you enter "lifetime reserve days," which are a limited number of extra days Medicare will cover in your lifetime, also with a daily copayment.

Part A also covers skilled nursing facility care, but only after a hospital stay. You must have been admitted to the hospital for at least three days, and you must move to a skilled nursing facility within 30 days of leaving the hospital. Medicare covers all costs for the first 20 days, then requires a daily copayment for days 21 through 100. After 100 days in a single benefit period, you pay all costs yourself.

Part A also covers hospice care if you are diagnosed with a terminal illness, and some home health services when ordered by your doctor and provided by a Medicare-approved agency. You typically pay nothing for these services, though you may pay a small copayment for prescription drugs or medical equipment used at home.

Medicare Part B: Doctor Visits and Outpatient Services

Part B covers doctor office visits, whether your doctor is a primary care physician or a specialist. It covers preventive services like annual wellness visits, cancer screenings, and vaccinations at no cost to you. It also covers outpatient hospital services, meaning care you receive at a hospital without being admitted overnight — such as emergency room visits, surgery centers, or imaging like X-rays and MRIs.

Part B covers medical equipment and supplies ordered by your doctor, including wheelchairs, walkers, oxygen, diabetic testing supplies, and hearing aids (though hearing aid coverage is limited). It covers mental health services, including therapy and psychiatry visits. It covers rehabilitation services like physical therapy and occupational therapy when medically necessary.

You pay a monthly premium for Part B — the amount depends on your income and changes each year. You also pay an annual deductible, and after you meet it, you typically pay 20 percent of the cost of most services while Medicare pays 80 percent. Some preventive services have no copayment or coinsurance.

Medicare Part D: Prescription Drug Coverage

Part D is prescription drug coverage offered by private insurance companies approved by Medicare. It is not automatic — you must choose a Part D plan and enroll during the annual enrollment period in the fall, or during a special enrollment period if you have a may have access to event like losing other drug coverage.

Each Part D plan has a different list of covered drugs, called a formulary, and different costs. Plans are required to cover drugs in certain categories, but they can charge different copayments or coinsurance for different drugs. Some drugs may require prior approval from the insurance company before they are covered. You can review and compare Part D plans on Medicare.gov, and you can change plans once per year during the enrollment period.

Part D has a coverage gap, sometimes called the "donut hole." Once you and your plan have paid a certain amount for drugs in a year, you enter the gap and pay a higher percentage of drug costs until you reach a spending threshold. After that, catastrophic coverage kicks in and you pay a small copayment for most drugs for the rest of the year. The exact amounts change each year.

Medicare Advantage (Part C): An All-in-One Alternative

Medicare Advantage, also called Part C, is a way to get your Part A and Part B coverage through a private insurance company instead of through Original Medicare. If you choose an Advantage plan, you do not pay Part A and Part B premiums separately — instead, you pay the Advantage plan's premium, which may be zero dollars per month. You still pay your Part B premium to Medicare, but the Advantage plan handles the rest.

Advantage plans must cover everything that Original Medicare covers, but they often add extra benefits like dental, vision, hearing, or fitness programs. Many Advantage plans include Part D prescription drug coverage built in. However, Advantage plans use a network of doctors and hospitals, and you usually pay more if you see a doctor outside the network. Some plans require referrals to see specialists.

Advantage plans often have lower out-of-pocket costs than Original Medicare for hospital and doctor visits, because they set annual limits on what you pay. However, you are locked into that plan's network unless you switch during the annual enrollment period. If you travel frequently or want to see any doctor who accepts Medicare, Original Medicare may be a better fit.

Costs and Coverage Gaps Across All Parts

Original Medicare (Parts A and B) does not cover everything. It does not cover routine dental care, vision exams, eyeglasses, hearing aids (with limited exceptions), or long-term care in a nursing home or at home. It does not cover most prescription drugs unless you add Part D. Many people buy a supplemental insurance plan, called Medigap, to cover costs that Original Medicare does not pay — such as copayments, coinsurance, and the Part B deductible.

If you choose Advantage instead, the plan's network and rules determine what you pay and where you can go for care. Advantage plans often cover services Original Medicare does not, but you give up the freedom to see any doctor who accepts Medicare. The trade-off is worth exploring if you have chronic conditions and want predictable costs, but it requires understanding the specific plan's rules before you enroll.

Costs for all parts change each year. Medicare announces new premiums, deductibles, and copayments in the fall, and they take effect January 1. You can review your coverage and make changes during the annual enrollment period from October 15 to December 7 each year.

When to Ask Your Doctor or Call Medicare

Ask your doctor which services you might need in the coming year — this helps you understand whether Original Medicare or Advantage is the better fit for you. If you have multiple chronic conditions or take many prescription drugs, your doctor can help you think through whether a plan with a network restriction makes sense.

Call Medicare directly at 1-800-MEDICARE (1-800-633-4227) if you have questions about what each part covers, what your costs will be, or whether you are enrolled in the right plan. Medicare staff can walk you through your options and answer specific questions about your situation. You can also visit Medicare.gov to compare plans, review coverage, and enroll in Part D or Advantage during the enrollment period.

Frequently Asked Questions

Do I have to take all four parts of Medicare?

No. Part A and Part B are automatic at 65 if you receive Social Security, but you can decline them if you have other coverage. Part D and Part C are optional — you choose whether to add them. If you do not choose Part D when you first become may be able to access and later want it, you may pay a penalty for each month you were without it.

What is the difference between Original Medicare and Advantage?

Original Medicare is fee-for-service coverage run by the federal government — you can see any doctor who accepts Medicare. Advantage is a private insurance plan that must cover the same services but uses a network and may require referrals. Advantage often costs less out-of-pocket but limits where you can go for care.

Can I switch from Advantage back to Original Medicare?

Yes, during the annual enrollment period from October 15 to December 7, you can switch from Advantage to Original Medicare or to a different Advantage plan. Changes take effect January 1. If you miss the important date, you are locked in until the next enrollment period, with limited exceptions.

Do I need Medigap if I have Original Medicare?

Medigap is optional but covers costs that Original Medicare does not pay, such as copayments and the Part B deductible. Whether you need it depends on your budget and how much medical care you expect to use. Advantage plans include cost limits, so Medigap is not available if you choose Advantage.

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

If you do not have other drug coverage and do not choose Part D, you can enroll later, but you may owe a late enrollment penalty for each month you were without it. The penalty is added to your Part D premium for as long as you have Medicare. It is usually cheaper to enroll in Part D when you first become may be able to access, even if you do not take many drugs yet.