CALIFORNIA MEDICARE GUIDE
Understand the main Medicare coverage paths
A plain-language introduction to Original Medicare, Medicare Advantage, and Medigap.
What are Medicare Parts A, B, C, and D?
Part A is hospital insurance and generally helps with inpatient hospital care, skilled nursing facility care, hospice, and some home health care. Part B is medical insurance for doctors, outpatient care, durable medical equipment, and many preventive services. Part C means Medicare Advantage, a private Medicare approved alternative that combines Part A and Part B and usually Part D. Part D is prescription drug coverage.
What is the difference between Original Medicare and Medicare Advantage?
Original Medicare is Part A and Part B administered by the federal program. You can generally use any doctor or hospital that takes Medicare; you can add a separate Part D plan and, if appropriate, Medigap. Medicare Advantage is a Medicare approved private plan that delivers Part A and Part B benefits and usually drug coverage. It may use networks, referrals, and prior authorization, and it has its own cost sharing and annual out of pocket limit.
What is Medigap, and how is it different from Advantage?
Medigap is private supplemental insurance that works with Original Medicare to help pay certain Medicare cost sharing. It does not work with Medicare Advantage and cannot pay its copays, deductibles, or premiums — to have Medigap you must be in Original Medicare, and you can generally leave Medicare Advantage only during specific allowed enrollment periods, not on any date you choose. Medigap plans are standardized by letter, although premiums and availability can vary. The best-protected time to buy is the six month Medigap Open Enrollment Period beginning when you are 65 or older and enrolled in Part B; outside that period, or a guaranteed-issue or trial right, an insurer can medically underwrite you and may deny coverage or charge more. If you move from Medicare Advantage back to Original Medicare plus Medigap, you may also need a separate Part D plan.
Three things to do next
- Understand how each coverage route works.
- Compare total costs, provider rules, prescriptions, and travel needs.
- Ask which products an insurance agent represents before considering an application.
Check the official sources
- Medicare: Parts of Medicare (opens in a new tab)
- Compare options (opens in a new tab)
- Medicare: Medigap timing (opens in a new tab)
- California DOI: Medigap guide (opens in a new tab)
We prepare these explanations from the listed sources. This is general education, not a personalized recommendation. Confirm current rules and individual dates with the appropriate official source. Our editorial approach.