What Is Medicare? Parts A, B, C and D Explained Simply

Medicare is the U.S. federal government's health insurance program for people 65 and older, and for some younger people with disabilities or end-stage kidney disease. It has four parts: Part A (hospital insurance), Part B (medical insurance), Part C (Medicare Advantage) and Part D (prescription drug coverage).

If you are turning 65 soon, or helping your parents make sense of their coverage, this guide walks through each part in plain language. At the end, you will find an English–Vietnamese glossary to make Medicare paperwork easier to share with Vietnamese-speaking family members.

What is Medicare?

Medicare is a federal program, which means it works the same way in all 50 states. Whether your parents live in California, Texas or Virginia, their basic Medicare benefits are the same.

Two agencies come up again and again:

• CMS (Centers for Medicare & Medicaid Services) is the federal agency that runs Medicare. It decides which services are covered and oversees the private insurance companies that offer Medicare plans.
• SSA (Social Security Administration) is where most people sign up for Medicare. People who already receive Social Security benefits before turning 65 are usually enrolled automatically.

In short, CMS runs the program and SSA handles enrollment.

Medicare is not entirely free. Depending on the part, you may pay a monthly premium, a deductible and a share of the cost for each service. These amounts change every year, so check the current figures at Medicare.gov.

Who is eligible for Medicare?

Most people on Medicare are 65 or older, but some younger people qualify too:

• People 65 and older who are U.S. citizens, or lawful permanent residents (green card holders) who meet the residency rules.
• People under 65 with a disability, usually after receiving Social Security Disability Insurance (SSDI) for 24 months.
• People with ALS (Lou Gehrig's disease) or end-stage renal disease (kidney failure requiring dialysis or a transplant), under separate waiting-period rules.

Premium-free Part A: Most people don't pay a monthly premium for Part A, because they or their spouse worked and paid Medicare taxes for about 10 years (40 quarters). People without enough work history can still enroll, but they pay a premium for Part A.

A note for non-citizens: A federal law passed in July 2025 narrowed which immigrants can enroll in Medicare. Green card holders without enough work history generally must have lived in the U.S. continuously for five years before enrolling. Because these rules changed recently, confirm your family's situation with SSA or a free counseling program (see the end of this article).

The four parts of Medicare

Medicare is divided into four parts, labeled A, B, C and D. Parts A and B come directly from the federal government. Parts C and D are offered by private insurance companies approved by Medicare.

Part A: Hospital insurance

Part A helps pay for inpatient hospital stays. It also helps cover some time in a skilled nursing facility after a hospital stay, hospice care and some home health care.

Part B: Medical insurance

Part B covers outpatient care: doctor visits, lab tests, imaging, preventive services such as screenings and vaccines, and some medical equipment. Most people pay a monthly premium for Part B. Learn more in What Does Medicare Part B Cover?

Part C: Medicare Advantage

Medicare Advantage plans are offered by private insurance companies as an alternative to Parts A and B. They must cover at least what Parts A and B cover, and most also include drug coverage (Part D). Many offer extra benefits such as dental, vision and hearing. People in Medicare Advantage usually still pay their Part B premium.

Part D: Prescription drug coverage

Part D helps pay for prescription drugs. It is offered by private companies, and each plan has its own list of covered drugs. You can buy a stand-alone Part D plan if you have Original Medicare, or get drug coverage through a Medicare Advantage plan that includes it. Learn more in What Is Medicare Part D?

The four parts at a glance

Part	Also called	Helps pay for	Offered by
A	Hospital insurance	Inpatient hospital stays, skilled nursing facility care, hospice	Federal government
B	Medical insurance	Doctor visits, outpatient care, preventive services	Federal government
C	Medicare Advantage	Replaces A and B, usually with drug coverage and extras	Medicare-approved private companies
D	Drug coverage	Prescription drugs	Medicare-approved private companies

Original Medicare vs. Medicare Advantage: what's the difference?

When you join Medicare, you choose one of two ways to get your benefits: Original Medicare (Parts A and B) or Medicare Advantage (Part C). Neither is better for everyone. What matters is which one fits your health needs, the doctors you already see and your budget.

Feature	Original Medicare	Medicare Advantage
Offered by	Federal government	Medicare-approved private insurance companies
Choice of doctors and hospitals	Any provider that accepts Medicare, nationwide	Usually within the plan's network (HMO, PPO)
Referral to see a specialist	Usually not needed	Required by many plans
Drug coverage	Buy a separate Part D plan	Usually included
Yearly limit on out-of-pocket costs	None, unless you buy Medigap	Yes, for Part A and Part B services
Extra benefits (dental, vision, hearing)	Mostly not covered	Offered by many plans
Can add Medigap	Yes	No

You can change your choice each year during Open Enrollment, from October 15 to December 7. Costs, doctor networks and drug lists for Medicare Advantage plans change from year to year, so it is worth reviewing your coverage every fall.

To compare plans where you live, use the plan finder on Medicare.gov, or get free, unbiased help from your state's SHIP program (called HICAP in California). Contact details are at the end of this article.

How is Medicare different from Medicaid?

The names sound alike, but they are two separate programs. Medicare is based mainly on age or disability. Medicaid is based mainly on income and assets.

Feature	Medicare	Medicaid
Who it's for	People 65 and older, some people with disabilities or end-stage kidney disease	People with limited income and assets, of any age
Who runs it	Federal government	Each state, with federal and state funding
Rules	The same nationwide	Vary by state
Local name	Medicare	Medi-Cal in California
Cost to the member	Usually premiums, deductibles and cost-sharing	Usually very low or none

Having both Medicare and Medicaid (dual eligible)

Some people qualify for both programs at the same time. They are called dual eligible. In that case, Medicare usually pays first. Medicaid then helps with what is left, such as the Part B premium, deductibles and cost-sharing, and may cover some services Medicare doesn't.

People with limited income who don't qualify for full Medicaid may still get help through Medicare Savings Programs, or through Extra Help, which lowers Part D drug costs. Ask your state Medicaid office or SSA whether your family qualifies.

English–Vietnamese Medicare glossary

Many Vietnamese-speaking parents rely on their children to explain Medicare letters. This glossary helps you translate the terms that come up most often.

English	Vietnamese	What it means
Original Medicare	Medicare Nguyên Thủy	Parts A and B, provided by the federal government
Medicare Advantage	Medicare Lợi Điểm (Phần C)	Private plans that replace Parts A and B
Part A / B / C / D	Phần A / B / C / D	The four parts of Medicare
Premium	Phí bảo hiểm	The amount you pay regularly, usually monthly, to have coverage
Deductible	Khoản khấu trừ	What you pay yourself before insurance starts to pay
Copayment (copay)	Khoản đồng trả	A fixed amount you pay for a service, such as each doctor visit
Coinsurance	Đồng bảo hiểm	Your share of the cost as a percentage, such as 20%
Out-of-pocket maximum	Mức trần tự trả	The most you pay in a year for covered services
Medigap	Bảo hiểm Bổ sung Medicare	Private insurance that helps pay what Original Medicare doesn't
Formulary	Danh sách thuốc	The drugs a plan covers
Network	Mạng lưới	Doctors and hospitals contracted with a plan
Referral	Giấy giới thiệu	A primary doctor's approval to see a specialist
Prior authorization	Chấp thuận trước	The plan must approve a service or drug before covering it
Initial Enrollment Period	Thời gian ghi danh lần đầu	The window around your 65th birthday to sign up
Open Enrollment	Mùa ghi danh mở	October 15 to December 7 each year, when you can change plans
Late enrollment penalty	Tiền phạt ghi danh trễ	Extra cost for signing up late without a qualifying reason
Dual eligible	Có cả Medicare và Medicaid	Qualifying for both programs
Extra Help	Trợ giúp Thêm	Help paying Part D drug costs for people with limited income
Medicare Summary Notice	Thông báo Tóm tắt Medicare	A statement of services Original Medicare has paid for
Beneficiary	Người thụ hưởng	A person who has Medicare

Medicare-covered services many people don't know about

Beyond doctor visits and hospital stays, Medicare also covers some ongoing care services. Many families have never heard of them, even though their parents may qualify.

Chronic care management (Part B)

People with two or more chronic conditions expected to last at least 12 months, such as high blood pressure, diabetes or heart disease, may qualify for Chronic Care Management (CCM). Each month, a care team member checks in on their health, reminds them about medications and coordinates with their doctor based on a care plan. CCM is covered by Part B, but the usual Part B deductible and coinsurance may apply. Supplemental coverage or Medicaid may help with that share. Learn more on Compass AgeWell's Chronic Care Management page.

Medication review with a pharmacist (through Part D)

Part D plans must offer Medication Therapy Management (MTM) to eligible members, usually people with several chronic conditions who take many medications. A pharmacist reviews everything they take, including over-the-counter medicines and supplements, to catch interactions and explain how to take each one. There is no extra cost for eligible members. Each Part D plan sets its own eligibility criteria. Learn more on Compass AgeWell's Medication Review page.

Telehealth visits

Medicare covers some visits by video or phone, just like in-person visits. Under rules extended by Congress, people with Medicare can currently have telehealth visits from home, anywhere in the U.S., through December 31, 2027. The usual Part B deductible and coinsurance still apply. See Does Medicare Cover Telehealth? and Compass AgeWell's Telehealth page.

Where to get free, unbiased help

You never need to pay anyone to explain Medicare. These sources are official or neutral, and none of them sell insurance:

Source	How it helps	Contact
Medicare	Benefits, current costs, plan comparison	Medicare.gov · 1-800-MEDICARE (1-800-633-4227)
Social Security Administration (SSA)	Enrolling in Medicare, checking work history	SSA.gov/medicare · 1-800-772-1213
SHIP (State Health Insurance Assistance Program)	Free, one-on-one, unbiased Medicare counseling	Find your local office at shiphelp.org
HICAP (California's SHIP program)	Free, confidential counseling; does not sell insurance	1-800-434-0222 · aging.ca.gov

Medicare also publishes materials in Vietnamese, including the yearly handbook Medicare & Quý vị ("Medicare & You"), which you can download or order free from Medicare.gov. When calling Medicare or SSA, you can ask for a free Vietnamese interpreter.

Frequently asked questions

Is Medicare free?

Not entirely. Most people pay no monthly premium for Part A because they paid Medicare taxes long enough. Part B, Part D and many Medicare Advantage plans have monthly premiums, plus deductibles and cost-sharing. People with limited income may get help from Medicaid or other assistance programs.

When should I sign up for Medicare?

Your Initial Enrollment Period lasts seven months: it starts three months before the month you turn 65, includes your birthday month, and ends three months after. Signing up late can mean a penalty that lasts as long as you have coverage. If you or your spouse are still working and have employer coverage, different rules may apply, so check with SSA before delaying.

Can green card holders get Medicare?

Yes, if they meet the requirements. Green card holders 65 and older can enroll. Those without about 10 years of work history generally must have lived in the U.S. continuously for five years before enrolling, and pay a premium for Part A. Rules for non-citizens changed in 2025, so confirm with SSA or your local SHIP/HICAP office.

Can I have Medicare and Medicaid at the same time?

Yes. People who qualify for both (dual eligible) have Medicare pay first, and Medicaid helps with the rest, such as premiums and cost-sharing. In California, Medicaid is called Medi-Cal.

Final thoughts

Medicare has many parts and a lot of jargon, but understanding it early helps your family avoid missing benefits your parents are entitled to. If your parents live with high blood pressure, diabetes or other chronic conditions, Medicare may cover regular monthly check-ins and a medication review with a pharmacist. When your family needs someone to explain things in Vietnamese, the Compass AgeWell team is always happy to talk.

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This article is for general information only and is not a substitute for advice from Medicare, SSA or a licensed insurance counselor. Compass AgeWell is a healthcare services provider. We are not a government agency, are not affiliated with Medicare or CMS, and do not sell insurance.

Sources: Medicare.gov · SSA – Parts of Medicare · KFF – Can immigrants enroll in Medicare? · California Department of Aging – HICAP · Medicare & Quý vị 2026