Medicare has four parts, and most people need more than one

Medicare is divided into four separate parts: Part A, Part B, Part D, and Part C. Part A and Part B are the original Medicare program run by the federal government. Part D covers prescription drugs. Part C, also called Medicare Advantage, is an alternative way to get Parts A and B through a private insurance company. You do not automatically get all four parts — you choose which ones you need based on your situation and what coverage you want.

Understanding what each part covers is the first step to knowing what you will pay for and what gaps might exist in your coverage. Many people find they need to add supplemental coverage (called Medigap) to cover costs that Medicare itself does not pay. This guide explains what each part does and how they work together.

Key Takeaways

  • Part A covers hospital stays, skilled nursing care, and hospice; Part B covers doctor visits and outpatient services; Part D covers prescription drugs; and Part C is a private alternative that bundles A and B together.
  • You are automatically enrolled in Part A and Part B when you turn 65 if you have worked and paid Medicare taxes, but you must actively choose Part D and decide whether to keep original Medicare or switch to Part C.
  • Original Medicare (Parts A and B) leaves you responsible for deductibles, copayments, and coinsurance, which is why many people buy Medigap coverage to fill those gaps.
  • Part C (Medicare Advantage) often costs less in premiums but typically requires you to use doctors and hospitals within a specific network, and it always includes prescription drug coverage.
  • Your choices during the initial enrollment period when you turn 65 affect your costs and coverage for the rest of the year, so understanding the differences before that window closes matters.

Part A: Hospital and skilled nursing coverage

Part A covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health services. If you are admitted to a hospital as an inpatient (not just for observation), Part A pays for your room, meals, and most hospital services after you pay a deductible. The deductible amount changes each year and applies per hospital stay, not per year.

Part A also covers up to 100 days in a skilled nursing facility if you are admitted after a hospital stay of at least three days. After day 20, you pay a daily copayment. Home health services — such as nursing care or physical therapy at home — are covered if a doctor orders them and you are homebound. Hospice care for people with a terminal illness is also covered, though you may pay small copayments for drugs and respite care.

Most people do not pay a premium for Part A because they or their spouse paid Medicare taxes while working. If you did not work long enough to may have access to for premium-free Part A, you can buy it, but the monthly cost varies based on how many years you worked.

Part B: Doctor visits and outpatient services

Part B covers doctor visits, outpatient care, diagnostic tests, and preventive services. This includes office visits with your primary care doctor or specialists, lab work, X-rays, and imaging. Part B also pays for durable medical equipment like wheelchairs, walkers, and oxygen, as well as mental health services and physical therapy.

You pay a monthly premium for Part B, and the amount depends on your income. Higher earners pay more. You also pay an annual deductible before Part B coverage kicks in, and then you typically pay 20 percent coinsurance for most services after that. Preventive services like annual wellness visits, cancer screenings, and vaccinations are covered at no cost to you.

Part B is not automatic — you must choose to enroll when you turn 65. If you delay enrollment without a valid reason, you may face a permanent penalty on your premium. The valid reasons include still being covered by employer health insurance or being a federal employee.

Part D: Prescription drug coverage

Part D covers prescription medications through private insurance plans approved by Medicare. It is not run by the government itself, but rather by insurance companies that contract with Medicare. You choose a Part D plan during your initial enrollment period, and the plan you pick determines which drugs are covered, what you pay, and which pharmacies you can use.

Part D plans have different costs and coverage rules. Most plans charge a monthly premium, and you pay a deductible before coverage begins. After that, you typically pay a copayment or coinsurance for each prescription. The amount you pay depends on which "tier" the drug is on — generic drugs usually cost less than brand-name drugs.

If you do not enroll in Part D when you first become may be able to access, you may face a permanent penalty if you go without creditable drug coverage for more than 63 days. Creditable coverage means coverage that is at least as good as Medicare's Part D. If you have drug coverage through a current employer or union, that may count as creditable coverage, so you would not face a penalty for delaying Part D.

Part C: Medicare Advantage as an alternative to original Medicare

Part C, also called Medicare Advantage, is a private insurance alternative to original Medicare. If you choose Part C, you get your Part A and Part B coverage through a private insurance company instead of the government. Part C plans always include Part D (prescription drug coverage), so you do not choose a separate drug plan.

Medicare Advantage plans often have lower or no monthly premiums compared to original Medicare plus Medigap, but they usually require you to use doctors and hospitals within their network. If you go out of network, you may pay more or the service may not be covered at all. Many plans also include extra benefits that original Medicare does not cover, such as dental, vision, or fitness programs.

The trade-off is that you may face higher copayments and coinsurance when you use services, and you need approval from the plan before certain procedures. If you choose Part C, you cannot also buy Medigap coverage. You can switch back to original Medicare during the annual open enrollment period, but if you have a pre-existing condition, switching plans can affect your coverage.

How the parts work together

If you choose original Medicare, you typically use Part A and Part B together. Part A covers hospital and skilled nursing care, while Part B covers outpatient services. You then choose a Part D plan for prescription drugs. Many people also buy Medigap coverage to pay the deductibles, copayments, and coinsurance that original Medicare does not cover.

If you choose Part C instead, the Medicare Advantage plan handles all of Part A and Part B coverage, and prescription drugs are included. You do not need Medigap because Part C is a complete alternative to original Medicare, not an addition to it.

Your choices during the initial enrollment period — the three months before and three months after you turn 65 — lock in your coverage for the rest of the year. If you miss this window, you may face higher premiums or gaps in coverage. You can make changes during the annual open enrollment period from October 15 to December 7, but not all changes are allowed outside the initial period.

Common gaps in Medicare coverage

Original Medicare does not cover everything. Dental care, vision care (including eyeglasses and contact lenses), hearing aids, and long-term care are not covered by any part of Medicare. You either pay out of pocket or buy separate insurance for these services. Some Medicare Advantage plans include dental or vision benefits, but coverage varies widely by plan.

Original Medicare also does not cover routine foot care, cosmetic surgery, or most acupuncture. If you travel outside the United States, original Medicare generally does not cover care you receive abroad, though some Medicare Advantage plans offer limited international coverage.

This is why many people who choose original Medicare buy Medigap coverage — to fill the gaps that Medicare itself leaves. Medigap plans are standardized and sold by private insurance companies, and they pay some or all of the costs that original Medicare does not cover, such as deductibles and coinsurance.

Frequently Asked Questions

Do I have to take all four parts of Medicare?

No. You are automatically enrolled in Part A and Part B at 65 if you may have access to, but you choose whether to enroll in Part D and whether to keep original Medicare or switch to Part C. If you have coverage through an employer or union, you may delay Part B or Part D without penalty.

What is the difference between original Medicare and Medicare Advantage?

Original Medicare (Parts A and B) is run by the government and lets you see any doctor who accepts Medicare. Medicare Advantage (Part C) is run by private insurance companies and usually requires you to use doctors in their network. Medicare Advantage often costs less in premiums but may have higher copayments and requires prior approval for some services.

Can I have both original Medicare and Medicare Advantage at the same time?

No. You choose one or the other. If you have original Medicare, you can add Medigap and Part D. If you have Medicare Advantage, it includes Part D and you cannot also buy Medigap.

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

If you go without creditable drug coverage for more than 63 days, you will pay a permanent penalty on your Part D premium for as long as you have Medicare. The penalty is calculated based on how long you went without coverage. If your employer or union provides drug coverage that is at least as good as Medicare's, you do not face a penalty for delaying Part D.

Can I change my mind about which parts of Medicare I want?

Yes, but timing matters. During the initial enrollment period (three months before and after you turn 65), you can make any changes. After that, you can make changes only during the annual open enrollment period from October 15 to December 7. Outside these windows, changes are limited and may result in higher premiums.