What Is Medicare?
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What Is Medicare?

What Is Medicare?
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Updated on October 15, 2026
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Medicare is a federal health insurance program for people ages 65 and older, as well as for those with certain disabilities. Currently, more than 70 million Americans are enrolled in the program.

Navigating the ins and outs of Medicare can be tricky, though, mainly because there are multiple parts to the program, each covering certain aspects of your care. To fill the gaps in your coverage, “You need to navigate supplemental benefits and prescription drug plans,” says Jennifer Wolff, PhD, a professor of health policy and management at the Johns Hopkins University Bloomberg School of Public Health in Baltimore. “It’s far trickier than choosing an employer-sponsored health plan.”

Once you understand the basics, you’ll feel more confident about making coverage decisions.

How Does Medicare Work?

Medicare is a federal health insurance program. What makes Medicare different from employer-based plans is that hospital coverage, physician services, and prescription coverage are split into separate parts. Each of these parts can have different enrollment deadlines, costs, and requirements.

Unlike standard health insurance plans, which bundle everything together, Medicare requires you to select and combine different pieces of coverage to meet your needs. There’s also Medicare Advantage (Part C), which is an alternative to Medicare that’s offered by a private insurance company.

Who Qualifies for Medicare?

Medicare is available for people ages 65 and older. However, you may be eligible at a younger age if you have a qualifying disability, end-stage renal disease (ESRD), or amyotrophic lateral sclerosis (ALS), also called Lou Gehrig’s disease. Your eligibility for Medicare is not based on your finances.

What Are the Different Parts, and Do I Need Them?

Medicare has four parts. Each covers different aspects of your healthcare:

  • Part A Hospital insurance
  • Part B Medical insurance
  • Part C Medicare Advantage
  • Part D Prescription drug coverage

Medicare parts A and B together are known as original Medicare, and Part D is a supplemental drug coverage program. Part C, Medicare Advantage, is an alternative to original Medicare. It provides all of parts A and B, usually Part D, and potentially other benefits. It will be covered in another section.

Medicare Part A: Hospital Insurance

Medicare Part A covers inpatient hospital care, skilled nursing care, hospice care, and some home healthcare services.

You may want to sign up for Medicare Part A as soon as you turn 65, even if you (or your spouse) have health insurance from a job. Some employers require you to take Part A when you’re eligible for it — and they may not cover your healthcare costs if you don’t. Just know that you can’t contribute to a health savings account (HSA) if you have Part A, so you should stop contributing about six months before you apply.

Medicare Part B: Medical Insurance

Medicare Part B covers doctors’ visits, outpatient care, medical equipment, and preventive services, such as annual checkups, glaucoma screenings, mammograms, vaccines, and screenings for various cancers.

You can choose to sign up for Part B after you (or your spouse) stop working or lose health insurance coverage. You have eight months to sign up without paying a penalty. If you have health insurance through an employer, you should check with them to see whether you have to enroll in Part B, since some employers require their employees to take Part B as soon as they’re eligible.

If you don’t have other insurance, you must sign up for Part B as soon as you’re eligible, or you will have to pay a penalty: 10 percent for each year you could have had Part B but didn’t enroll. You have to pay this penalty for as long as you have Part B.

Medicare Part D: Prescription Drug Coverage

Medicare Part D covers the cost of prescription medications and certain vaccines.

Enrollment in Part D is voluntary, but unless you have additional health insurance coverage — from an employer, for example — you’ll likely want to sign up. Part D can help offset the cost of prescription drugs, and delaying your enrollment can result in a permanent financial penalty (an extra 1 percent per month).

How Much Will It Cost Me?

Medicare isn’t free — something that often takes people by surprise, says Josh Hodges, chief impact officer at the National Council on Aging. The cost can vary based on income, location, and coverage choices, but here’s the general breakdown for the monthly premiums in 2026:

  • Part A Usually free
  • Part B Starts at $202.90 monthly
  • Part D Averages $34.50 monthly for stand-alone plans, with a $2,100 annual out-of-pocket maximum

Along with monthly premiums, Medicare parts A, B, C, and D may also have deductibles, coinsurance, and copays.

To help pay for these out-of-pocket expenses, many people with Medicare choose to have supplemental coverage, such as Medigap (see below). People with limited income can also be eligible for assistance programs, such as the Medicare Part D Extra Help program, which helps pay for the costs of prescription drugs, says Kata Kertesz, JD, the managing policy attorney for the Center for Medicare Advocacy.

There’s also the Medicare Savings Program, which helps pay for Part A and Part B. The Qualified Medicare Beneficiary Program Group also provides Part A and Part B premiums and cost sharing to low-income Medicare beneficiaries.

What Is Medigap Coverage?

Because original Medicare has no out-of-pocket maximum and requires you to pay 20 percent of medical costs for Part B services, many people purchase supplemental insurance called Medigap. These policies, sold by private insurers, help cover Medicare’s deductibles, copays, and coinsurance. Premiums vary by plan type, location, and insurer, but they averaged around $217 a month in 2023.

Where and How Do I Sign Up?

There are a several ways to sign up for Medicare, depending on whether you have disabilities, are retired, or are still working:

  • If you have ALS, you’ll automatically be enrolled in Medicare parts A and B when your disability payments start. If you receive Social Security disability benefits, you’ll be automatically enrolled after 24 months of receiving disability benefits. If you have ESRD, you can choose whether to enroll in Medicare; your coverage can start retroactively (up to 12 months before you sign up).

  • If you receive Social Security benefits for at least four months before you turn 65, you’ll be automatically enrolled in Medicare Part A and Part B when you turn 65.
  • If you apply for Social Security benefits when you turn 65, you can sign up for Medicare at that time.
  • If you’re still working and want to delay your Social Security benefits, you can apply online for Medicare or may be able to wait until you retire.

You can sign up for Medicare online at SSA.gov/Medicare/sign-up, or call 800-772-1213.

You can only enroll in Medicare at certain times, including:

  • Initial Enrollment Period This seven-month period includes the three months before your 65th birthday, your birthday month, and three months after. This is usually the first chance to sign up for Medicare.

  • General Enrollment Period This period lasts from January 1 to March 31, with coverage starting the month after you apply. If you missed your initial enrollment period, you can enroll during the general enrollment period.
  • Special Enrollment Period You can sign up for Medicare within eight months of losing employer coverage or six months of losing Medicaid.

  • Open Enrollment Period If you already have Medicare, you can change coverage from original Medicare to a Medicare Advantage plan, change Medicare Advantage plans, or join or switch Part D plans from October 15 to December 7. Coverage begins January 1.

  • Medicare Advantage Open Enrollment Period If you’re already in a Medicare Advantage plan, you can switch to a different plan or drop the plan and switch to original Medicare (and a separate drug plan) from January 1 to March 31. During this period, you can’t switch from original Medicare to a Medicare Advantage plan.

How Does Medicare Work if I Have Retiree Insurance?

If your former employer offers retiree health coverage, it will work together with Medicare to pay for your healthcare. Usually, Medicare pays first while retiree insurance kicks in to help pay for deductibles, copays, and coinsurance.

Retiree health coverage may also include coverage for vision and dental that Medicare doesn’t cover. Sometimes, retiree health coverage provides creditable drug coverage, so you may not need to sign up for Part D. Check with your plan first, though; in some cases, signing up for Part D will cause you to lose your retiree coverage.

What Is Medicare Advantage?

Medicare Advantage (Part C) plans bundle all your Medicare coverage into one private insurance plan. Most Medicare Advantage plans combine parts A, B, and D coverage with additional benefits, like dental, vision, hearing, and fitness programs.

While every Medicare Advantage plan must cover all medically necessary services that original Medicare covers, plans differ in their costs, rules, and network of providers. Medicare Advantage plans have a maximum out-of-pocket limit of $9,250 for in-network care in 2026. Original Medicare doesn’t have an out-of-pocket maximum.

For example, most Medicare Advantage plans require prior authorization for certain services, referrals to see specialists, and require you to use healthcare providers and hospitals in the plan’s network.

“Medicare Advantage plans vary tremendously across the country, and what you ultimately choose often depends on your health needs,” says Wolff.

How Do I Know if My Current Doctors Will Accept Medicare?

Most U.S. doctors accept Medicare.

To find a list of doctors in your area who take Medicare, you can use Medicare’s find and compare tool. Select “Providers & Services” from the menu on the left side of the page. Look for providers noted as charging the Medicare-approved amount.

If a doctor accepts the Medicare-approved amount, they will not be able to bill you for more than that. If a doctor takes Medicare but doesn’t accept the Medicare-approved amount, they can charge up to 15 percent more.

You can also call the doctor’s office directly or call Medicare at 800-633-4227.

What Is a Medicare Secondary Payer?

If you have Medicare and another type of health insurance (like retiree coverage or Medicaid), there’s an order to how bills get paid.

The “primary payer” pays first, up to the limits of its coverage, then the “secondary payer” jumps in to help cover the remaining balance.

While Medicare is often the primary payer, there are times when another insurer must pay first, making Medicare the secondary payer. Medicare will pay second if:

  • You work at a company with 20 or more employees and you’re 65 or older (or are covered through your spouse’s current employer’s plan)
  • You’re under 65 years old, have a disability, and have coverage through an employer with 100 or more employees
  • You’re within the first 30 months of ESRD treatment
  • Workers’ compensation is paying
  • You were in an auto accident (no-fault or liability insurance) and their no-fault or liability insurance company is paying
  • You have COBRA (only in certain situations)

FAQ

What’s the difference between Medicare and Medicaid?

Medicare is a federal health insurance program for people ages 65 and older, as well as people with certain disabilities, regardless of income. Medicaid is a joint federal and state health insurance plan for people with limited incomes, regardless of age.

Yes. While Part A is usually premium-free if you or your spouse paid Medicare taxes for 10 years, Part B has a monthly premium that’s typically deducted from Social Security (if you’re getting Social Security payments). Parts C and D may also have monthly premiums that vary by plan.

To qualify for Medicare, you must be at least 65 years old, or be under 65 and have a qualifying disability, end-stage renal disease, or amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease.

Resources We Trust

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Medicare Monthly Enrollment. Centers for Medicare & Medicaid Services. September 23, 2026.
  2. Which Path Is Right for Me? Medicare.gov.
  3. Parts of Medicare. Medicare.gov.
  4. Get Started With Medicare. Medicare.gov.
  5. What Original Medicare Covers. Medicare.gov.
  6. Working Past 65. Medicare.gov.
  7. 5 Things You Need to Know About Signing Up for Medicare. Centers for Medicare & Medicaid Services. March 10, 2026.
  8. Preventive & Screening Services. Medicare.gov.
  9. What Part B Covers. Medicare.gov.
  10. How Do Drug Plans Work? Medicare.gov.
  11. What’s Medicare Drug Coverage (Part D)? Medicare.gov.
  12. Medicare Costs. Medicare.gov.
  13. Medicare Advantage and Medicare Prescription Drug Programs Expected to Remain Stable in 2026. Centers for Medicare & Medicaid Services. September 26, 2025.
  14. Qualified Medicare Beneficiary (QMB) Program Group. Centers for Medicare & Medicaid Services. March 16, 2026.
  15. Medicare Savings Program. Medicare.gov.
  16. Apply for Medicare Part D Extra Help Program. Social Security.
  17. Key Facts About Medigap Enrollment and Premiums for Medicare Beneficiaries. KFF. October 18, 2024.
  18. How and When to Apply for Medicare. USAGov.
  19. I’m Getting Social Security Benefits Before 65. Medicare.gov.
  20. End-Stage Renal Disease (ESRD). Medicare.gov.
  21. When Does Medicare Coverage Start? Medicare.gov.
  22. Medicare Open Enrollment. Centers for Medicare & Medicaid Services. March 4, 2026.
  23. Medicare & You 2027. Medicare.gov.
  24. Retiree Insurance & Medicare. Medicare.gov.
  25. Retiree Insurance and Medicare Coordination. Medicare Interactive. March 23, 2025.
  26. Freed M et al. Medicare Advantage in 2026: Premiums, Out-of-pocket Limits, Supplemental Benefits, and Prior Authorization. KFF. June 5, 2026.
  27. How Can I Find Out if My Doctor Accepts Medicare? KFF. October 9, 2026.
  28. Does Your Provider Accept Medicare as Full Payment? Medicare.gov.
  29. How Medicare Works With Other Insurance. Medicare.gov.
  30. Medicare Secondary Payer. Centers for Medicare & Medicaid Services. September 10, 2024.
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