Understanding Medicare Eligibility and How Coverage Works

What Medicare Is and Who It Serves

Medicare is a federal health insurance program run by the Centers for Medicare & Medicaid Services (CMS). It was created in 1965 and currently serves more than 66 million Americans. Unlike private health insurance that individuals purchase from insurance companies, Medicare is a government-operated program funded through payroll taxes and general revenues.

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The program was designed to help people pay for hospital care, doctor visits, prescription medications, and other medical services. Medicare covers hospital stays, outpatient procedures, doctor appointments, preventive care, medical equipment, and certain prescription drugs. However, it does not cover all medical expenses—items like dental work, vision care, hearing aids, and long-term custodial care are generally not included.

Medicare serves several distinct populations. The largest group includes people age 65 and older, regardless of income or work history. A second group includes some younger people with permanent disabilities who have received Social Security disability benefits for at least 24 months. A third group includes people with end-stage renal disease (permanent kidney failure requiring dialysis or transplant) and amyotrophic lateral sclerosis (ALS, also called Lou Gehrig's disease).

The program consists of different parts, each covering different services. Part A covers hospital care, Part B covers doctor services and outpatient care, Part D covers prescription drugs, and Part C (Medicare Advantage) is an alternative way to receive Parts A and B coverage. Understanding which parts cover which services is important for knowing what costs you may face.

Understanding the basics of Medicare helps people make informed decisions about their health coverage. Many people are surprised to learn that Medicare does not cover every medical expense, and some people choose to buy additional coverage (called "Medigap" or "supplemental" insurance) to cover gaps in Medicare's coverage. Learning how Medicare works and what it covers is the first step toward managing healthcare costs in retirement or while dealing with a disability.

Practical Takeaway: Medicare is a federal insurance program for people 65 and older, some younger people with disabilities, and people with certain serious conditions. It has multiple parts that cover different types of care, but it does not cover all medical expenses.

Understanding the Four Parts of Medicare

Medicare is divided into four distinct parts, and each part covers different healthcare services. Understanding what each part covers helps people understand their coverage and out-of-pocket costs.

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Part A – Hospital Insurance covers inpatient hospital stays, skilled nursing facility care (short-term care after a hospital stay), hospice care, and some home health services. For example, if someone has a heart attack and spends five days in the hospital, Part A would help pay for that hospital stay. If after being released, they need skilled nursing care to recover, Part A would cover a portion of that care for up to 100 days. Part A is funded through a payroll tax paid by workers and employers—people who worked for at least 10 years generally do not pay a monthly premium for Part A.

Part B – Medical Insurance covers doctor services, outpatient care, diagnostic tests, and preventive services. This includes office visits with doctors, lab tests, X-rays, surgical procedures performed in outpatient settings, mental health services, and physical therapy. Part B also covers preventive services like annual wellness visits, cancer screenings, and vaccinations. Most people pay a monthly premium for Part B, which in 2024 ranges from approximately $163 to $560 per month depending on income. Part B also requires people to pay a deductible (currently $240 per year) before coverage begins.

Part D – Prescription Drug Coverage helps pay for prescription medications. This part is offered by private insurance companies approved by Medicare. People choose a Part D plan that covers the medications they use, and plans vary in terms of which drugs they cover and how much people pay. Part D coverage has a deductible (currently $545 per year), a coverage gap (sometimes called the "donut hole"), and different cost-sharing amounts depending on which medications are used. For example, a person taking diabetes and blood pressure medications might pay $15 to $50 per month depending on their chosen plan.

Part C – Medicare Advantage is an alternative to Parts A and B offered by private insurance companies. Instead of traditional Medicare, people can choose a Medicare Advantage plan that covers their hospital and doctor visits through the private insurer. Medicare Advantage plans often include prescription drug coverage (Part D) and may offer additional benefits like dental, vision, or fitness programs. However, Medicare Advantage plans typically have smaller networks of doctors and hospitals, and they may charge higher out-of-pocket costs for certain services.

Many people use traditional Medicare (Parts A, B, and D) and buy a supplemental insurance policy (Medigap) to help cover deductibles, copayments, and other costs. Others choose Medicare Advantage for the additional benefits and simpler coverage structure. Understanding the differences between these options helps people choose coverage that matches their health needs and budget.

Practical Takeaway: Medicare has four main parts: Part A covers hospital care, Part B covers doctor services, Part D covers prescription drugs, and Part C is a private insurance alternative. Each part covers different services and has different costs.

Who Can Receive Medicare Coverage

Most people think of Medicare as coverage for people age 65 and older, but the program serves other populations as well. Knowing whether someone can receive Medicare coverage depends on factors including age, work history, citizenship, and certain medical conditions.

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People Age 65 and Older form the largest group of Medicare recipients. A person generally becomes covered by Medicare at age 65 if they or their spouse worked for at least 10 years in jobs where Medicare taxes were withheld from paychecks. This 10-year work history does not have to be continuous—it can be scattered throughout a person's career. Government employees hired before 1983 or railroad workers may have different requirements. U.S. citizens and permanent residents (green card holders) who meet the work history requirement can receive Medicare at 65. Undocumented immigrants are not covered by Medicare.

People Under 65 With Disabilities can receive Medicare if they have received Social Security disability benefits for at least 24 months. This includes people with physical disabilities, mental health conditions, developmental disabilities, and other medical conditions that prevent them from working. For example, a 40-year-old with rheumatoid arthritis who has received disability benefits for two years would become covered by Medicare. Additionally, people who are blind and receive Social Security benefits may be covered regardless of how long they have received benefits.

People With End-Stage Renal Disease (ESRD) become covered by Medicare regardless of age or work history. ESRD means permanent kidney failure requiring dialysis treatment or a kidney transplant. Dialysis is an expensive treatment that filters waste from blood, and Medicare coverage for these individuals helps ensure access to this necessary care. A person with ESRD becomes covered by Medicare after they start dialysis treatment or receive a kidney transplant.

People With Amyotrophic Lateral Sclerosis (ALS) become covered by Medicare immediately upon receiving an ALS diagnosis, without needing to wait for disability benefits. ALS is a progressive neurological disease that gradually weakens muscles. Because the disease is rapidly progressive and fatal, Medicare coverage begins right away to help people access the medical care they need.

To receive Medicare, people must also be U.S. citizens or permanent residents. They must also complete certain administrative steps, though the specific requirements vary depending on their situation. People who receive Social Security benefits are often automatically enrolled in Medicare Parts A and B at age 65. Others may need to take action to receive coverage.

Practical Takeaway: Medicare covers people age 65 and older with work history, younger people with disabilities receiving Social Security benefits, people with permanent kidney failure, and people with ALS. U.S. citizenship or permanent residency is required.

How to Begin Medicare Coverage and What to Do

The process for beginning Medicare depends on a person's situation. Understanding the timing and steps involved helps people avoid gaps in coverage or late enrollment penalties.

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People Receiving Social Security Benefits at age 65 are usually automatically enrolled in Parts A and B. These individuals receive a Medicare card in the mail about three months before they turn 65. They do not need to take additional action unless