Medicare Explained: What It Is, What It Covers, and How It Works

If you’re approaching age 65, already on Social Security, or helping a parent with their coverage, Medicare can feel like an alphabet soup of Parts A, B, C, and D. Understanding the basics now makes it much easier to avoid gaps in coverage and unexpected costs later.

What Is Medicare?

Medicare is a federal health insurance program mainly for:

• People 65 and older
• Certain younger people with disabilities
• People with End-Stage Renal Disease (ESRD) or ALS

It helps pay for hospital care, doctor visits, preventive services, and prescription drugs. Medicare is not completely free: you’ll still have premiums, deductibles, copays, and coinsurance, but it usually costs less than buying similar coverage on your own at that age.

The Four Parts of Medicare

Medicare is divided into four main parts, each covering different services:

Part A – Hospital Insurance
Helps cover:

• Inpatient hospital stays
• Skilled nursing facility care (short-term, after a qualifying hospital stay)
• Some home health care and hospice care

Most people don’t pay a Part A premium if they worked and paid Medicare taxes long enough, but there are deductibles and coinsurance for each benefit period.

Part B – Medical Insurance
Helps cover:

• Doctor visits and outpatient care
• Preventive services (like flu shots and screenings)
• Durable medical equipment (like walkers or oxygen equipment)

Part B has a monthly premium and an annual deductible, then usually coinsurance (often 20% of the Medicare-approved amount) for most services.

Part C – Medicare Advantage
Medicare Advantage plans are private plans that contract with Medicare. They:

• Replace Original Medicare (Parts A and B) for your day‑to‑day use
• Often include Part D drug coverage
• May offer extra benefits like vision, dental, or hearing

You still stay in the Medicare program, but you use the plan’s network and rules (like HMOs or PPOs) rather than going directly through Original Medicare.

Part D – Prescription Drug Coverage
Stand-alone drug plans (for people in Original Medicare) or built into many Medicare Advantage plans. They:

• Cover many outpatient prescription medications
• Have their own premium, formulary (drug list), and cost tiers

You pay some combination of premiums, deductibles, copays, and coinsurance, depending on the plan.

How Enrollment and Coverage Work Together

Most people can first sign up during a 7‑month Initial Enrollment Period starting three months before the month they turn 65. Delaying Part B or Part D without other qualifying coverage can lead to late enrollment penalties that may last as long as you have Medicare.

At a high level, you choose between:

• Original Medicare (Parts A & B)

  • Optionally add a Part D drug plan
  • Optionally add a Medigap (Medicare Supplement) policy from a private insurer to help cover deductibles and coinsurance

• Medicare Advantage (Part C)

  • Combines A and B, usually D, and sometimes extra benefits
  • You pay according to the plan’s rules, networks, and cost-sharing

You can generally make coverage changes once a year during the Medicare Open Enrollment Period in the fall, with other special opportunities when your circumstances change.

Understanding what each part covers, what you’ll pay, and when you can enroll is the foundation of getting Medicare right. Once you grasp these basics, you can more confidently compare options—Original Medicare vs. Medicare Advantage, adding drug coverage, and deciding whether you need a Medigap plan—to build coverage that fits your health needs and budget.