Article 14 min

How Medicare Works: Parts A, B, C, and D Made Simple

Medicare is a federal health insurance program that helps many people manage health care costs as they get older (or if they qualify earlier due to certain disabilities or conditions). It can help pay for hospital stays, doctor visits, and prescription drugs, but it doesn’t cover everything—and some parts come with premiums, deductibles, and other out-of-pocket costs.

Summary

🧩 Medicare basics: what it is and what it covers

Medicare is the federal government’s health insurance program for Americans age 65 and older, as well as some younger people who qualify due to certain illnesses or disabilities. Medicare can help cover inpatient care (like hospital stays), outpatient care (like doctor visits and preventive services), and prescription drugs. It’s not a one-size-fits-all program, though: Medicare is divided into different “parts,” and each part covers a different category of care. While some people pay $0 for certain parts, Medicare is not completely free—many people have monthly premiums, plus deductibles, copays, or coinsurance depending on the coverage they choose.

Takeaways:

• Medicare is a federal health insurance program with multiple parts that cover different types of care.
• It can reduce major medical costs, but you should still plan for premiums and out-of-pocket expenses.
• Choosing the right setup depends on your health needs, budget, and provider preferences.

Key Terms

• Original Medicare: The government-run combination of Part A (hospital) and Part B (medical).
• Premium: The monthly amount you pay for coverage (some parts may be $0 for many people).
• Coinsurance: Your share of the cost for covered services, often a percentage (like 20%).

🧾 The four parts of Medicare

Medicare has four main parts: Part A, Part B, Part C, and Part D. Part A generally covers hospital care and related services. Part B generally covers doctor appointments and outpatient medical care. Part C, also called Medicare Advantage, is an alternative way to receive Part A and Part B benefits through private insurance companies (and it usually includes Part D). Part D covers prescription drugs through private plans. On top of that, some people with Original Medicare add Medigap (Medicare Supplement Insurance) to help cover certain out-of-pocket costs that Parts A and B don’t fully pay.

Takeaways:

• Parts A and B make up Original Medicare, while Part C (Medicare Advantage) is a private-plan alternative.
• Part D is prescription drug coverage and may be separate (Original Medicare) or bundled (often with Advantage).
• Medigap can help pay “gaps” in Original Medicare, but it doesn’t pair with Medicare Advantage.

Key Terms

• Part A: Hospital insurance that covers inpatient care and certain related services.
• Part B: Medical insurance that covers outpatient care, doctor visits, and many preventive services.
• Part D: Prescription drug coverage offered through private plans.

✅ Medicare eligibility: who can get it

You’re generally eligible for Medicare if you’re 65 or older and a U.S. citizen or permanent resident. Some people qualify before 65 if they have a qualifying disability or condition. People who receive Social Security Disability Insurance (SSDI) usually become eligible for Medicare after a two-year waiting period. People with end-stage renal disease (ESRD) are enrolled based on specific kidney and dialysis requirements, and people with ALS are eligible the month disability benefits begin. Because timing and qualification rules can vary depending on your situation, it helps to know which category you fall into before you decide when and how to enroll.

Takeaways:

• Most people qualify at 65, but some qualify earlier due to disability or specific conditions.
• SSDI recipients commonly face a two-year waiting period before Medicare eligibility begins.
• Eligibility timing affects when you can enroll and whether penalties may apply.

Key Terms

• SSDI: Social Security Disability Insurance, which can lead to Medicare eligibility after a waiting period for many recipients.
• ESRD: End-stage renal disease (permanent kidney failure), which can qualify someone for Medicare under specific rules.
• ALS: Amyotrophic lateral sclerosis, which can qualify someone for Medicare starting when disability benefits begin.

🏥 Original Medicare vs. Medicare Advantage: how coverage works

Original Medicare is Part A and Part B managed by the federal government. With Original Medicare, you can generally see any provider that accepts Medicare, and fewer services require preauthorization. Medicare Advantage (Part C) is offered by private insurers and replaces Original Medicare for your Part A and Part B benefits. With Medicare Advantage, you typically use a provider network to get the most affordable care, and you may need referrals to see specialists or preauthorization for certain services. You can have Original Medicare or Medicare Advantage, but not both. If you choose Original Medicare, you can usually add a standalone Part D plan and you may also add Medigap; if you choose Medicare Advantage, Part D is usually included and Medigap can’t be added.

Takeaways:

• Original Medicare is government-managed and often offers broader provider choice if the provider accepts Medicare.
• Medicare Advantage is private insurance, usually with networks, referrals, and preauthorization rules.
• Your choice determines what add-ons are available: Part D and Medigap work with Original Medicare, while Advantage plans typically bundle drug coverage.

Key Terms

• Medicare Advantage: A private plan alternative that covers Part A and Part B benefits and often includes Part D.
• Network: A group of doctors and hospitals that contract with a plan, often affecting your costs and access.
• Preauthorization: A plan requirement to get approval before certain services are covered.

🧠 Medicare Part A and Part B: what they cover and what they cost

Part A generally covers inpatient care in a hospital or skilled nursing facility (but not custodial or long-term care), plus hospice care and some home health care. Many people pay $0 for Part A if they (or their spouse) worked and paid Medicare taxes for at least 10 years; otherwise, Part A premiums can be up to $518 per month in 2025 ($565 in 2026). Part A also includes a deductible and hospital coinsurance that increases after longer stays. Part B covers doctor visits and other medically necessary services, including preventive care, ambulance services, durable medical equipment, mental health coverage, and certain outpatient prescription drugs. Part B has a monthly premium (at least $185 per month in 2025; $202.90 in 2026), a deductible, and typically 20% coinsurance for Medicare-approved services. Part B may also include a permanent late-enrollment penalty for people who delay enrollment without qualifying job-based coverage, and higher-income households may pay more due to IRMAA.

Takeaways:

• Part A focuses on hospital-related inpatient care, while Part B focuses on doctors and outpatient services.
• Even if your Part A premium is $0, you may still have a deductible and coinsurance costs.
• Part B commonly includes premiums, a deductible, and 20% coinsurance, and late enrollment can trigger a lasting penalty.

Key Terms

• Deductible: The amount you pay before coverage begins paying its share for certain services.
• IRMAA: An income-related adjustment that can increase what higher earners pay for Part B (and Part D).
• Medicare-approved services: Care and supplies that Medicare recognizes and helps cover under its rules.

🪪 Medicare Part C and Part D: private plans, extra benefits, and prescription coverage

Medicare Advantage (Part C) plans are offered by private insurers and provide Part A and Part B benefits, usually Part D prescription coverage, and sometimes extra benefits such as some dental and vision coverage. These plans are often structured as HMOs or PPOs, which can affect whether you need referrals, how your out-of-pocket costs work, and which doctors and hospitals are considered in-network. Costs vary by plan: some plans have $0 premiums (though you still pay the Part B premium), and they include deductibles and cost-sharing that can differ widely. Part D plans, also offered by private insurers, help cover prescription drugs and require a monthly premium. Like Part B, higher-income individuals may pay more, and late enrollment can trigger a penalty if you go without creditable drug coverage for 63 days after you’re eligible.

Takeaways:

• Medicare Advantage often bundles hospital, medical, and prescription drug coverage into one plan, plus possible extras.
• Networks and plan rules (like referrals or preauthorization) can meaningfully affect access and costs.
• Part D is prescription coverage with plan-specific premiums and a potential late-enrollment penalty if you delay without creditable coverage.

Key Terms

• HMO/PPO: Common plan types that influence provider access, referrals, and how costs are shared.
• Creditable drug coverage: Prescription coverage considered comparable to Medicare Part D, used to avoid late penalties.
• Copayment: A set dollar amount you may pay for certain services or prescriptions under a plan.

🧩 Medigap: filling coverage gaps in Original Medicare

Medigap (also called Medicare Supplement Insurance) is additional coverage you can buy from a private insurer to help pay certain costs that Medicare Part A and Part B don’t cover, such as deductibles and coinsurance. Medigap plans are standardized (for example, Plan G offers the same base benefits across states, though pricing can differ), and there are 10 plan types available in most states. To buy Medigap, you must have Part A and Part B, and you can’t have Medicare Advantage at the same time. Some plans that covered the Part B deductible (Plan C and Plan F) aren’t available to new Medicare members. Medigap premiums vary widely, and certain plans include out-of-pocket limits (like Plan K and Plan L), while others may not.

Takeaways:

• Medigap is designed to reduce out-of-pocket costs in Original Medicare, such as coinsurance and certain deductibles.
• You can pair Medigap with Original Medicare, but not with Medicare Advantage.
• The best fit depends on your budget, expected care needs, and how much cost predictability you want.

Key Terms

• Medigap: A private supplemental policy that helps pay certain costs not fully covered by Parts A and B.
• Standardized plan: A plan whose base benefits are the same by letter type, even if prices vary by location.
• Out-of-pocket limit: A cap on what you pay for covered services in a year under certain plan types.

💵 What Medicare can cost: premiums and out-of-pocket expenses

Medicare costs depend on which coverage you choose. Part A is typically $0 for most people, while Part B is typically $185 per month in 2025. Medicare Advantage premiums vary and can be $0, though you still pay Part B; the average Part C premium is listed as $17 in 2025. Part D premiums vary by plan, with an average total monthly premium of $38 in 2025, plus deductibles and copays that depend on your plan’s design. Medigap premiums also vary by plan type and location, and some people may pay more for Parts B and D if their income is above certain thresholds. Beyond premiums, deductibles and cost-sharing can add up, and Original Medicare generally does not have an annual cap unless you have Medigap.

Takeaways:

• Medicare can lower big medical bills, but monthly premiums and cost-sharing are still common.
• Costs vary significantly depending on whether you choose Original Medicare, Medicare Advantage, Part D, and/or Medigap.
• Understanding premiums, deductibles, and coinsurance helps you budget more confidently for health care.

Key Terms

• Premium: What you pay each month to keep coverage active.
• Coinsurance: A percentage of costs you may pay for covered services (for example, 20% under Part B).
• Deductible: What you pay before certain benefits begin to pay their share.

📝 How to enroll in Medicare (and when to add Part D or Medigap)

How you enroll depends on whether you’re already receiving Social Security when you turn 65. If you are, you’ll be automatically enrolled in Part A and Part B. To get Part D, you generally must sign up (unless you get a notice that you qualify for Extra Help, in which case you may be automatically enrolled unless you already joined a plan). If you’re not receiving Social Security when you turn 65, you must sign up for Medicare through the Social Security Administration website or by calling Social Security at 800-772-1213—typically during your initial enrollment period to avoid penalties. If you want Medigap, the six-month Medigap open enrollment period starts the month you are age 65 or older and enrolled in Part B; during that time, insurers are required to take you, but outside that window they may deny coverage or charge more. If you want to change coverage later, there’s an annual Medicare open enrollment period from Oct. 15 to Dec. 7, and Medicare Advantage members may also have a separate window from Jan. 1 to March 31 each year to make certain changes.

Takeaways:

• If you’re already receiving Social Security at 65, Part A and Part B enrollment is typically automatic.
• If you’re not receiving Social Security, you generally need to actively enroll to avoid late penalties.
• Timing matters for Medigap: the open enrollment window can make it easier to get a policy without higher costs or denial.

Key Terms

• Initial enrollment period: The first window when many people should enroll to avoid late penalties.
• Medigap open enrollment: A six-month window when insurers generally must sell you a Medigap policy if you qualify.
• Open enrollment period: A yearly window when you can review and change certain Medicare coverage choices.

🚫 What Medicare doesn’t cover (and why it matters)

Medicare doesn’t cover everything, and some common expenses can surprise people if they assume they’re included. Coverage gaps can include most dental care, hearing aids, eyeglasses, dentures, and medical care overseas. Medicare also doesn’t cover long-term care. Some frequently excluded items include hearing aids and fitting exams, eye exams and eyeglasses, dentures, most dental care, most foot care (unless related to diabetes or medically necessary due to injury or disease), medical care overseas, cosmetic surgery, and massage therapy. These gaps are a big reason some people explore Medicare Advantage extra benefits, consider separate dental/vision coverage, or budget specifically for services that won’t be reimbursed.

Takeaways:

• Medicare commonly excludes routine dental, vision, and hearing needs, plus most overseas care and long-term care.
• Knowing what isn’t covered helps you avoid surprise expenses and plan for additional coverage if needed.
• Your best strategy may include comparing plan benefits carefully and setting aside savings for known gaps.

Key Terms

• Long-term care: Ongoing assistance with daily activities that Medicare generally does not cover.
• Supplemental coverage: Additional insurance that can help with services or costs not covered by your primary plan.
• Out-of-pocket costs: Expenses you pay yourself, such as deductibles, copays, coinsurance, and non-covered services.

🧭 Where to get help choosing the right Medicare setup

Because Medicare choices can feel complex, getting reliable guidance can be a big relief—especially when you’re comparing Original Medicare, Medicare Advantage, Part D plans, and Medigap options. Your local State Health Insurance Assistance Program (SHIP) can help you understand coverage choices and how they apply to your situation. Medicare.gov is the official Medicare website, and you can also live chat or call 800-MEDICARE (800-633-4227, TTY 877-486-2048) for general support. If you’re sorting through enrollment timing, plan rules, costs, or coverage gaps, using these resources can help you feel more confident about the trade-offs and your next steps.

Takeaways:

• Medicare decisions are easier when you use trusted, official resources and local counseling support.
• Comparing costs, provider access, and drug coverage side-by-side can prevent expensive surprises later.
• Getting help early can make enrollment and plan selection feel much less overwhelming.

Key Terms

• SHIP: A State Health Insurance Assistance Program that offers Medicare counseling and education.
• Provider access: Whether your doctors, hospitals, and pharmacies are covered and affordable under your plan’s rules.
• Plan comparison: Reviewing benefits, costs, and coverage limits to find the best match for your needs.

Conclusion

Medicare can be a powerful tool for managing health care costs, but it works best when you understand the different parts, how eligibility and enrollment timing affect you, and what costs you may still pay. By comparing Original Medicare, Medicare Advantage, Part D, and Medigap (when applicable), you can build coverage that fits your health needs and budget—while avoiding common gaps and late-enrollment penalties.