Medicare is the federal health insurance program for Americans aged 65 and older, as well as some younger people with qualifying disabilities. It is one of the most important benefits in the American system, but its lettered parts can be confusing at first. This guide explains Parts A, B, C, and D in plain language, along with enrollment basics and costs to expect.
Who Qualifies for Medicare?
Most people qualify for Medicare when they turn 65 if they or their spouse paid Medicare taxes through work for a sufficient number of years. Younger people can qualify after receiving Social Security disability benefits for a set period, and people with end-stage kidney disease or amyotrophic lateral sclerosis (ALS) may qualify under special rules.
Medicare is not the same as Medicaid. Medicare is mainly age- and disability-based and is run by the federal government. Medicaid is income-based and run jointly by the federal government and the states. Some people with limited incomes qualify for both programs, and Medicaid can help pay Medicare premiums and cost-sharing in those cases.
You do not automatically receive all parts of Medicare without taking action. Some parts begin automatically if you already receive Social Security benefits, but in other cases you must enroll during an enrollment window. Missing a deadline can lead to late-enrollment penalties, so understanding the timeline matters.
Part A: Hospital Insurance
Part A covers inpatient hospital care, skilled nursing facility care after a qualifying hospital stay, hospice care, and some home health care. Most people pay no monthly premium for Part A because they or their spouse paid Medicare taxes while working. People who do not qualify for premium-free Part A may be able to buy it by paying a monthly premium.
Part A has a deductible for each hospital benefit period, and longer hospital stays can involve daily coinsurance after a certain number of days. It does not cover long-term custodial care in a nursing home, which is a common misunderstanding. Custodial care, meaning help with everyday activities such as bathing and eating when that is the only care needed, is generally not covered by Medicare.
Part B: Medical Insurance
Part B covers outpatient care: doctor visits, preventive services, lab tests, durable medical equipment, mental health services, and many other medical services received outside a hospital stay. Most people pay a monthly premium for Part B, and the amount can be higher for people with higher incomes.
Part B also has an annual deductible. After the deductible, you generally pay a percentage of the approved cost for most services. Because there is no annual out-of-pocket maximum in Original Medicare, many people add supplemental coverage to limit their exposure to large bills, which is discussed below.
Preventive care is a major benefit of Part B. Many screenings, vaccinations, and annual wellness visits are covered at no cost to you when the service meets Medicare's rules, which makes Part B valuable even for healthy beneficiaries.
Part C: Medicare Advantage
Part C, known as Medicare Advantage, is an alternative way to receive Medicare benefits through a private plan approved by Medicare. These plans must cover everything that Parts A and B cover, and most also include prescription drug coverage and extra benefits such as dental, vision, hearing, or fitness programs.
Medicare Advantage plans work through networks, similar to private health plans. You may need to use network doctors and hospitals, and you may need referrals to see specialists, depending on the plan type. Premiums, copayments, and out-of-pocket maximums vary by plan and by area, and plans are offered locally, so the options in one county can differ from those in another.
Choosing between Original Medicare and Medicare Advantage is a personal decision. Original Medicare offers broad access to providers across the country, while Medicare Advantage often offers lower premiums and extra benefits but a more limited network. You can generally switch between them during the annual Medicare open enrollment period.
Part D: Prescription Drug Coverage
Part D covers prescription drugs through private plans approved by Medicare. You can get Part D as a stand-alone plan alongside Original Medicare, or as part of a Medicare Advantage plan that includes drug coverage.
Each Part D plan has its own list of covered drugs, called a formulary, organized into tiers with different copayments or coinsurance. Checking that your regular medicines are covered, and at what cost, is essential before choosing a plan. Plans also have a deductible and coverage phases, and costs can change if a drug moves tiers or if you enter a different phase of coverage.
People who delay enrolling in Part D when first eligible, and who do not have other creditable drug coverage, may face a late-enrollment penalty added to their premium for as long as they have Part D. Keeping proof of other drug coverage, such as through an employer plan, is therefore important.
Supplemental Coverage and Costs
Original Medicare leaves gaps: deductibles, coinsurance, and the lack of an out-of-pocket maximum. Many beneficiaries fill these gaps with a Medigap policy, also called Medicare Supplement Insurance, which is sold by private companies and helps pay some of the costs that Original Medicare does not. Medigap policies are standardized by letter, but premiums vary by insurer and location.
The best time to buy a Medigap policy is usually during the six-month period that starts when you are 65 or older and enrolled in Part B. During this window, insurers generally cannot deny you or charge more because of health problems. After that window, buying Medigap can be harder or more expensive, depending on your state's rules.
Total Medicare costs therefore include Part B premiums, any Part D or Medicare Advantage premium, Medigap premiums if you buy one, plus deductibles and copayments. Reviewing your coverage each year during open enrollment is wise, because plan costs, formularies, and networks change annually.
Conclusion
Medicare's four parts each play a distinct role: Part A for hospital care, Part B for medical services, Part C as a private-plan alternative, and Part D for prescription drugs. Understanding what each part covers, when to enroll, and how supplemental coverage works helps you avoid penalties and unexpected costs. Take time to compare your options each year, and seek free, unbiased counseling from your state's health insurance assistance program if you need help deciding.
Frequently Asked Questions
When should I sign up for Medicare?
Your initial enrollment period generally runs for seven months around your 65th birthday. If you already receive Social Security benefits, Parts A and B may start automatically; otherwise you need to enroll yourself.
Does Medicare cover everything?
No. Original Medicare does not cover most dental, vision, and hearing care, nor long-term custodial care. Many people add a Medicare Advantage plan, Medigap policy, or separate coverage for those needs.
Can I change my Medicare plan later?
Yes. During Medicare open enrollment each fall, you can switch between Original Medicare and Medicare Advantage, change Medicare Advantage plans, or join or change a Part D plan.
What is the Part D late-enrollment penalty?
If you go without creditable prescription drug coverage for a continuous period after first becoming eligible, a penalty may be added to your Part D premium permanently, so enroll on time or keep proof of other coverage.