Medicare Parts

What Is Medicare? Parts A, B, C and D in Plain English

By Tai Thao, Licensed Independent Medicare Agent, Golden Milestone Services · Updated October 23, 2026

Medicare has four familiar labels—Part A, Part B, Part C and Part D—but they do not represent four separate policies that everyone must buy. Part A and Part B make up Original Medicare. Part C, also called Medicare Advantage, is another way to receive Medicare benefits. Part D helps with prescription drug coverage. Knowing which part does what is the starting point for understanding your choices in Wisconsin.

The letters are easier to understand when you connect them to real questions: Who pays when I am admitted to a hospital? What about a doctor visit? How would I receive my benefits through a private Medicare plan? And where does prescription coverage fit?

What is Medicare, and who can get it?

Medicare is federal health insurance generally available to eligible people age 65 or older. Some people qualify before 65 because of a disability or certain medical conditions, including end-stage renal disease or ALS. Eligibility and the time to enroll depend on personal circumstances. Medicare is individual coverage, so spouses do not have to choose the same way of receiving their benefits.

Think of Medicare in two stages. First, determine when and how you receive Part A and Part B. Then decide whether to keep Original Medicare or receive your benefits through Medicare Advantage. Prescription coverage and any supplemental coverage are decisions connected to that second stage.

What does Medicare Part A cover?

Part A is hospital insurance. It generally helps cover inpatient hospital care, eligible skilled nursing facility care, hospice care and certain home health services. It is not a blanket promise to cover every service performed in a hospital building. For example, whether a stay is classified as inpatient or outpatient can affect which Medicare part applies. Coverage also depends on Medicare's conditions for the service.

A common misunderstanding is that Part A covers ongoing custodial care simply because someone needs help with daily activities. Medicare's skilled nursing benefits have specific requirements; long-term custodial care is different.

What does Medicare Part B cover?

Part B is medical insurance. It helps cover medically necessary services from doctors and other health care providers, outpatient services, durable medical equipment and many preventive services. A clinic visit, certain tests or equipment used at home may involve Part B rather than Part A. Medicare sets rules about covered services and the conditions for receiving them.

Part B is not simply 'everything outside a hospital.' The setting, service and billing status can matter. Part B also does not mean every health expense disappears. Under Original Medicare, people generally remain responsible for a share of approved costs unless other coverage or assistance applies.

How do Part A and Part B work together?

Together, Part A and Part B are called Original Medicare. They cover different categories of medically necessary care and many preventive services. With Original Medicare, you generally can see any doctor or hospital in the United States that accepts Medicare. You can also consider separate prescription drug coverage and, if eligible, coverage that helps with your share of approved expenses.

Original Medicare is a way of receiving benefits, not a single card that automatically includes every kind of insurance. Check what coverage you actually have rather than assuming every letter is already included.

What is Medicare Part C, or Medicare Advantage?

Part C is Medicare Advantage. It is a Medicare-approved option offered by private insurance companies for receiving Part A and Part B benefits. Most Medicare Advantage plans also include Part D prescription drug coverage. You must have both Part A and Part B to join a Medicare Advantage plan, and you continue to be in Medicare.

How care is arranged can differ from Original Medicare. Depending on the plan type, you may need to use a provider network, request referrals or receive prior authorization for certain services. Medicare Advantage plans have an annual limit on covered out-of-pocket costs for Part A and Part B services.

Do not confuse Medicare Advantage with a Medicare Supplement policy. Advantage is a way to receive Medicare benefits. A supplement works alongside Original Medicare instead of replacing the way you receive Part A and Part B services.

What does Medicare Part D cover?

Part D is Medicare prescription drug coverage. It is offered through Medicare-approved private plans. If you use Original Medicare, you can generally join a separate Part D drug plan. If you use Medicare Advantage, drug coverage is usually included in the Medicare Advantage plan, although there are exceptions. Joining a separate drug plan when you already have certain Medicare Advantage coverage can change your health coverage, so check before making that move.

Prescription coverage has its own rules, including lists of covered drugs and pharmacy arrangements. A medication being prescribed does not by itself mean every Part D option handles it the same way. When reviewing drug coverage, make a current list of medications and pharmacies and check how the coverage you are considering treats them. Medicare also has rules about creditable drug coverage and late enrollment penalties, which can matter if you delay enrolling.

Is Medigap the same thing as Part C or Part D?

No. Medicare Supplement Insurance, commonly called Medigap, is not another Medicare part. It is separate insurance designed to help with certain costs left to you under Original Medicare. It does not turn Original Medicare into Medicare Advantage, and it does not substitute for Part D prescription drug coverage.

Wisconsin has its own approach to Medigap policy standardization, so do not assume that a chart of federal lettered Medigap plans describes Wisconsin policies. If you are considering supplemental coverage, review Wisconsin-specific information and your enrollment rights before making a decision. You generally cannot use Medigap to pay Medicare Advantage plan costs.

How do I choose between Original Medicare and Medicare Advantage?

Start with how you want to receive care, not a list of advertised extras. Under Original Medicare, the ability to use providers nationwide who accept Medicare can be important. With Medicare Advantage, the network and plan rules for routine care deserve close attention. Either way, ask whether your doctors and facilities are available under the arrangement you are considering and how prescription coverage will work.

Next, look at how you would handle your share of covered expenses, what happens when you travel, and whether you have coverage through an employer, union, Medicaid or another source. If you already have other insurance, Medicare coordination rules may affect which coverage pays first.

Are Medicare and Medicaid the same program?

No. Medicare is federal health insurance based primarily on age or qualifying disability or medical conditions. Medicaid is a federal-state program with eligibility rules tied to circumstances such as income and other factors. Some people qualify for both. Having both programs can affect how certain Medicare expenses are paid, but it does not change the basic meaning of Parts A, B, C and D.

What should I check before I sign up for Medicare?

First, confirm your enrollment timing through Medicare or Social Security. Some people are enrolled automatically, while others need to apply. If you or your spouse are still working and have job-based coverage, ask about the rules before delaying Part B. Timing mistakes can create gaps or penalties, and the correct answer depends on the type of coverage you have.

Second, write down your doctors, prescriptions, preferred pharmacies and any other insurance. Third, decide whether you are comparing ways to receive Medicare benefits or looking at supplemental and drug coverage alongside Original Medicare. Those are different questions. You can use Medicare's official information to check the rules and speak with a licensed agent about your situation without assuming that one arrangement works for everyone.

Where can I learn more about Medicare in Wisconsin?

Begin with Medicare's official explanations of the parts of Medicare and how coverage works. For enrollment questions, use the Medicare sign-up guide or Social Security. If you are comparing Original Medicare with Medicare Advantage, read the official coverage-options page first. Wisconsin residents considering a supplement should also check state-specific Medigap guidance. Understanding these basics makes later decisions about enrollment windows, prescriptions and coverage types much easier to discuss.