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Medicare Basics: Parts A, B, C, and D

A starter guide to Medicare coverage parts, enrollment timing, and how Medicare Advantage differs from Original Medicare.

By James Chen1 min read

The four main parts

Medicare is federal health insurance primarily for people 65 and older and certain younger individuals with disabilities. It is split into parts that cover different services.

  • Part A: Hospital insurance (inpatient stays, skilled nursing, hospice)
  • Part B: Medical insurance (doctor visits, outpatient care, preventive services)
  • Part C: Medicare Advantage (private plans that bundle Part A and B, often Part D)
  • Part D: Prescription drug coverage

When to enroll

Your Initial Enrollment Period starts three months before the month you turn 65 and ends three months after. Missing it can mean late enrollment penalties on Part B and Part D.

If you still work and have employer coverage, you may qualify for a Special Enrollment Period when that coverage ends.

Original Medicare vs Medicare Advantage

Original Medicare lets you see any provider that accepts Medicare nationwide. You can add a separate Part D plan and optional Medigap supplemental insurance.

Medicare Advantage plans often include drug coverage and extra benefits like dental, but use provider networks and may require referrals. Compare total cost and drug formularies carefully.

Where to learn more

Use Medicare.gov plan finder tools and your State Health Insurance Assistance Program (SHIP) for free, unbiased counseling. InsuLife comparison articles can help you frame questions before those conversations.

About the author

James Chen

Insurance Research Lead

James reviews plan documents, state marketplace rules, and employer benefit summaries. His goal is to help readers spot the details that change real out-of-pocket costs.

  • B.S. Economics, UCLA
  • Certified Health Insurance Specialist (CHIS)

Sources and references