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

Medicare Part A covers hospital stays, skilled nursing care, and hospice. Part B covers doctor visits and outpatient services. Part D covers prescription drugs. Part C, also called Medicare Advantage, is an alternative to Parts A and B offered by private insurance companies.

You do not automatically get all four parts. Part A and Part B are the foundation — most people over 65 get Part A for free, but you have to sign up for Part B and pay a monthly premium. Part D is separate and optional but costs less if you sign up when you first become may be able to access. Part C replaces Part A and B with a private plan, so you choose either Original Medicare (A and B) or Part C, not both.

The parts overlap in confusing ways. For example, Part B covers some preventive care that Part A does not. Part C includes drug coverage built in, while Original Medicare users need Part D separately. Understanding what each part does — and what it does not — determines how much you pay and what doctors and pharmacies you can use.

Key Takeaways

  • Part A covers hospital and skilled nursing stays; Part B covers doctor visits and outpatient care; Part D covers prescription drugs; Part C is a private alternative to A and B.
  • You get Part A automatically at 65 if you have worked and paid Medicare taxes, but you must sign up for Part B during your enrollment window or pay a penalty later.
  • Part D and Part C are optional, but delaying Part D enrollment can result in a permanent monthly surcharge if you go without coverage.
  • Original Medicare (Parts A and B) works with any doctor or hospital that accepts Medicare; Part C plans restrict you to in-network providers and often have lower premiums but higher out-of-pocket costs.

Part A: Hospital, Skilled Nursing, and Hospice Coverage

Part A pays for inpatient hospital stays, up to 100 days in a skilled nursing facility after a hospital stay, and hospice care. It does not cover outpatient doctor visits, routine care, or long-term nursing home care that is not skilled nursing.

You pay a deductible for each hospital stay — the amount changes yearly and is higher than Part B's deductible. After you meet the deductible, Medicare covers all costs for days 1 through 60. Days 61 through 90 require a daily coinsurance payment from you. Days 91 and beyond are covered only if you use your "lifetime reserve days," which are limited and do not renew each year.

Most people do not pay a monthly 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, you can buy Part A coverage, but the monthly premium is substantial — the exact amount depends on how many years you or your spouse worked.

Part B: Doctor Visits, Outpatient Care, and Preventive Services

Part B covers doctor office visits, emergency room care, lab tests, X-rays, and outpatient surgery. It also covers preventive services like annual wellness visits, cancer screenings, and vaccinations at no cost to you. Part B does not cover routine dental, vision, or hearing care.

You pay a monthly premium for Part B — the standard amount changes yearly, and higher-income retirees pay more. You also pay a yearly deductible before Part B coverage begins. After you meet the deductible, you typically pay 20 percent of the cost for most services, and Medicare pays 80 percent. For some services like office visits, you may pay a fixed copay instead.

You must sign up for Part B during your Initial Enrollment Period, which starts three months before the month you turn 65 and ends three months after. If you delay without a valid reason, you pay a permanent penalty — an extra 10 percent of your Part B premium for each year you were may be able to access but did not sign up. The only exception is if you are still working and covered by your employer's health plan; in that case, you can delay without penalty.

Part D: Prescription Drug Coverage

Part D covers prescription medications at pharmacies. It is run by private insurance companies under contract with Medicare, so the drugs covered, the pharmacies you can use, and the cost vary by plan. You choose a Part D plan during your enrollment period, and plans change their drug lists yearly.

Part D has a specific cost structure. You pay a monthly premium, then a yearly deductible (which varies by plan). After the deductible, you pay a percentage of the drug cost or a fixed copay, depending on the plan and the drug's tier. Once you and your plan together spend a certain amount on drugs in a year, you enter the "donut hole" — a gap where you pay more out of pocket. After you spend enough in the donut hole, catastrophic coverage kicks in and you pay a small copay for the rest of the year.

Like Part B, if you delay Part D enrollment without a valid reason, you pay a permanent penalty — an extra amount added to your monthly premium for each month you were may be able to access but not enrolled. The penalty applies even if you later sign up. If you have coverage through an employer or union, you may be able to delay without penalty, but you need to confirm this with your plan.

Part C: Medicare Advantage as an Alternative to Parts A and B

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 and extra benefits like dental or vision. If you choose Part C, you do not use Original Medicare (Parts A and B) — you use the Part C plan instead.

Part C plans often have lower or zero monthly premiums than Original Medicare, but they restrict you to in-network doctors and hospitals. If you see an out-of-network provider, you pay more or the plan does not cover it at all. Many plans require referrals to see specialists. Out-of-pocket costs can be higher than Original Medicare if you use a lot of care.

You can switch between Original Medicare and Part C during the annual Open Enrollment Period, which runs from October 15 to December 7 each year. Changes take effect January 1. If you choose Part C, you still need to be enrolled in Part A and Part B, but you use the Part C plan's benefits instead of Original Medicare's.

How the Parts Work Together: Original Medicare vs. Medicare Advantage

Most people choose either Original Medicare (Parts A and B, with Part D added separately) or Part C (Medicare Advantage). You cannot use both at the same time.

With Original Medicare, you can see any doctor or hospital that accepts Medicare — there are no networks. You pay the deductibles and coinsurance described above. You buy Part D separately from a private insurer. You may want to buy a Medigap policy (supplemental insurance) to cover some of the costs Medicare does not pay, like coinsurance and deductibles.

With Part C, the private plan handles all your coverage. Premiums are often lower, but you are locked into the plan's network. You cannot use Medigap. If you travel or move, you may need to switch plans. Part C plans often include dental, vision, and hearing benefits that Original Medicare does not.

Enrollment Periods and important date

Your first chance to sign up for Medicare is your Initial Enrollment Period, which is seven months long: three months before the month you turn 65, the month you turn 65, and three months after. If you miss this window, you can still sign up during the General Enrollment Period from January 1 to March 31 each year, but you may pay penalties.

Every year, the Annual Enrollment Period (also called Open Enrollment) runs from October 15 to December 7. During this time, you can change from Original Medicare to Part C, from Part C to Original Medicare, or switch Part C plans. You can also change Part D plans. Changes take effect January 1.

If you have a may have access to life event — such as losing employer coverage, moving out of your plan's service area, or getting married — you may be able to sign up or change plans outside the regular enrollment periods. You usually have 60 days from the event to make changes.

Frequently Asked Questions

Do I have to take all four parts of Medicare?

No. You must have Part A and Part B to have Medicare at all, but you choose either Original Medicare (A and B) or Part C. Part D is optional but recommended — if you do not take it when first may be able to access and later enroll, you pay a permanent penalty. Part C includes drug coverage, so Part C enrollees do not need separate Part D.

What happens if I miss my enrollment important date?

For Part B, you pay a permanent 10 percent penalty on your monthly premium for each year you delayed. For Part D, you pay a permanent penalty on your monthly premium for each month you were may be able to access but not enrolled. These penalties stay with you for life. You can still enroll during the General Enrollment Period (January 1 to March 31), but the penalties explore.

Can I switch from Part C back to Original Medicare?

Yes, during the Annual Enrollment Period (October 15 to December 7) or if you have a may have access to life event. If you switch back to Original Medicare, you can also sign up for Part D or a Medigap policy at that time. Some Medigap policies have waiting periods, so switching back can be more expensive than staying with Part C.

Does Part A or Part B cover dental, vision, or hearing?

Original Medicare (Parts A and B) does not cover routine dental, vision, or hearing care. Part C plans often include these benefits, though coverage varies by plan. You can buy standalone dental, vision, or hearing plans to supplement Original Medicare.

What is the difference between a copay and coinsurance?

A copay is a fixed dollar amount you pay for a service — for example, $25 for a doctor visit. Coinsurance is a percentage of the cost you pay after meeting your deductible — for example, 20 percent of the cost of an X-ray. Original Medicare typically uses coinsurance; Part C plans often use copays.