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

Medicare 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, lab tests, and medical equipment. Part C (Medicare Advantage) is an alternative way to get Parts A and B through a private insurance company. Part D covers prescription drugs. Most people who turn 65 need to sign up for Parts A and B, and many also choose Part D. Part C is optional and replaces Parts A and B if you choose it.

The parts do not overlap completely, and gaps exist. For example, Part A and Part B together do not cover dental, vision, or hearing aids. Understanding what each part does — and what it does not — helps you figure out what coverage you actually need.

Key Takeaways

  • Part A covers hospital and skilled nursing stays; Part B covers doctor visits and outpatient services; Part D covers prescription drugs.
  • Part C (Medicare Advantage) is a private insurance alternative that bundles Parts A and B, usually with lower out-of-pocket costs but a smaller network of doctors.
  • Most people are automatically enrolled in Part A at 65 if they have been paying Social Security taxes, but you must sign up for Part B during your enrollment window or face a permanent penalty.
  • Original Medicare (Parts A and B) has no network restrictions, so you can see any doctor who accepts Medicare anywhere in the country.
  • Gaps in all four parts exist — dental, vision, hearing, and long-term care are not covered by any Medicare part.

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 the first three days of a hospital stay if you have been there before, but you pay a deductible (the amount changes each year) for days 4 through 60. Days 61 through 90 cost you a daily amount. Beyond 90 days, you have 60 lifetime reserve days you can use, and after that, you pay the full cost yourself.

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, but the monthly cost is high. Part A is automatic at 65 if you are already getting Social Security; otherwise, you must sign up when you turn 65.

Part B: Doctor Visits and Outpatient Services

Part B covers doctor office visits, emergency room visits, outpatient surgery, lab tests, X-rays, physical therapy, and durable medical equipment like wheelchairs and oxygen. It also covers preventive services such as annual wellness visits, cancer screenings, and vaccinations at no cost to you. Part B does require a monthly premium, which is deducted from your Social Security check if you are receiving benefits.

You also pay a yearly deductible before Part B starts paying its share. After you meet the deductible, you typically pay 20 percent of the cost for most services, and Medicare pays 80 percent. However, you must see a doctor who accepts Medicare assignment — most do, but it is worth checking before your visit. If you do not sign up for Part B when you first turn 65, you will owe a permanent penalty (a higher monthly premium for life) unless you have other health insurance that covers the same services.

Part C: Medicare Advantage as an Alternative

Part C, also called Medicare Advantage, is a private insurance plan that covers everything Part A and Part B cover, plus usually Part D (prescription drugs) and sometimes dental or vision. You do not pay the Part B premium to Medicare; instead, you pay a premium to the private insurance company, which is often lower or even zero. However, you must use doctors and hospitals in that plan's network, except in emergencies.

Part C plans often have lower out-of-pocket costs than Original Medicare (Parts A and B) for people who use a lot of health care, but they restrict where you can go. If you travel frequently or want to see any doctor anywhere, Original Medicare may suit you better. Part C plans change their networks and benefits every year, so you need to review your plan during the annual enrollment period (October 15 to December 7) to make sure your doctors are still in the network.

Part D: Prescription Drug Coverage

Part D covers prescription medications. If you choose Original Medicare (Parts A and B), you must decide whether to add Part D. You can buy Part D from any insurance company that offers it, and plans vary widely in which drugs they cover and what you pay. Some drugs are covered at a lower cost; others are not covered at all. You pay a monthly premium for Part D, and you also pay a deductible before the plan starts paying.

If you do not sign up for Part D when you first turn 65 and you do not have other prescription drug coverage, you will owe a permanent penalty (a higher monthly premium) for as long as you have Medicare. If you choose Part C (Medicare Advantage), Part D is usually included, so you do not buy it separately. It is worth comparing Part D plans every year during open enrollment because the drugs you take may move to a different tier (cost level) or a plan may stop covering them altogether.

What Medicare Does Not Cover

None of the four parts cover dental care, vision care (eyeglasses and exams), or hearing aids. Long-term care in a nursing home or assisted living is also not covered. Cosmetic surgery, routine foot care, and most acupuncture are not covered. Some people buy a Medigap policy (supplemental insurance) to fill gaps in Original Medicare, or they choose Part C, which sometimes includes dental and vision benefits.

If you need long-term care, you would need to pay out of pocket, use Medicaid (a separate program for people with low income), or have purchased long-term care insurance before you turned 65. Understanding these gaps early helps you plan for costs that Medicare will not pay.

How to Sign Up and When

You become may be able to access for Medicare at 65. If you are already getting Social Security, you are automatically enrolled in Part A and Part B, and you will receive your Medicare card in the mail about three months before your 65th birthday. If you are not getting Social Security, you must sign up for Medicare yourself at Medicare.gov or by calling 1-800-MEDICARE.

Your initial enrollment window 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 and do not have other health insurance that covers the same services, you will owe a permanent penalty on your Part B and Part D premiums. Part C and Part D have their own enrollment rules and important date, which change each year. The annual open enrollment period for all Medicare plans runs from October 15 to December 7.

Frequently Asked Questions

Do I have to take all four parts of Medicare?

No. Part A is automatic at 65 if you may have access to. Part B is optional but recommended; if you skip it, you pay a penalty later. Part C is optional and replaces Parts A and B if you choose it. Part D is optional, but if you do not take it when first may be able to access and do not have other drug coverage, you pay a penalty.

What is the difference between Original Medicare and Medicare Advantage?

Original Medicare (Parts A and B) has no network — you can see any doctor anywhere. Medicare Advantage (Part C) is a private plan with a network, usually lower out-of-pocket costs, but you must use in-network doctors except in emergencies. Medicare Advantage plans change every year.

If I have Part C, do I still need Part D?

Most Part C plans include prescription drug coverage (Part D), so you do not buy Part D separately. Check your plan documents to confirm. If your Part C plan does not include drug coverage, you can add Part D.

What happens if I miss the sign-up important date for Part B or Part D?

You will owe a permanent penalty — a higher monthly premium for as long as you have Medicare. The only exception is if you had other health insurance that covered the same services during the time you were not enrolled.

Does Medicare cover dental, vision, or hearing aids?

No. None of the four parts cover routine dental, vision, or hearing aids. Some Part C plans offer limited dental or vision benefits, but coverage is usually minimal. You can buy a separate Medigap policy to cover some gaps, or pay out of pocket.