Quick Answer
Original Medicare combines Part A hospital insurance and Part B medical insurance. Medicare Advantage, or Part C, delivers those benefits through an approved private plan. Part D covers outpatient prescription drugs. Medigap supplements eligible costs left by Original Medicare and does not replace Medicare or cover Medicare Advantage cost sharing.
First identify the person's coverage route, then identify the service, provider rules, and remaining eligible cost.
What Does Each Medicare Part Do?
| Coverage | Main role |
|---|---|
| Part A | Inpatient hospital facility care and qualifying skilled nursing facility, hospice, and home health care |
| Part B | Physician services, outpatient care, qualifying home health care, durable medical equipment, and many preventive services |
| Part C | Medicare Advantage route through an approved private plan; drug coverage and extra benefits vary |
| Part D | Outpatient prescription drug coverage through a stand-alone plan or an Advantage plan that includes it |
- A formal inpatient admission points to Part A facility care. Outpatient observation remains outpatient, and a physician's professional service generally falls under Part B even during an inpatient stay.
- A Part A benefit period ends after 60 consecutive days without inpatient hospital care or qualifying skilled inpatient care. A new benefit period can bring a new inpatient deductible.
- For most covered Part B physician services, the patient generally pays 20% of the Medicare-approved amount after the deductible. Accepting assignment means the provider accepts that approved amount as full payment, subject to applicable patient cost sharing.
How Do Original Medicare and Medicare Advantage Differ?
- Original Medicare means Parts A and B. A person can add stand-alone Part D and may buy a Medigap policy.
- Medicare Advantage supplies Parts A and B through private-plan terms. Use the current Evidence of Coverage for services and cost sharing, the current provider directory for participating providers, and the plan's authorization rules before care.
- A provider's network status and approval of a particular service are separate facts. A doctor's order does not automatically satisfy prior authorization.
How Does Medigap Work?
- Original Medicare pays first for a covered service. Medigap then applies its own benefit to eligible remaining deductibles, copayments, or coinsurance. It does not pay every unpaid bill.
- Each policy covers one person. Spouses need separate policies.
- Where letter standardization applies, the same plan letter has the same basic benefits, but insurers can charge different premiums. Different letters provide different packages: standard Plan G and standard Plan N are not equivalent merely because their premiums match.
- Federal Medigap Open Enrollment lasts six months beginning with the first month the person is both at least 65 and enrolled in Part B. During that period, an insurer cannot deny an offered policy or charge more for pre-existing health problems through medical underwriting.
- That protection does not erase a permitted pre-existing-condition waiting period. Outside it, underwriting can apply unless a guaranteed-issue or other right controls.
How Should Drug and Provider Choices Be Compared?
- Part A and Part B do not establish Part D enrollment. A Medigap policy does not establish it either.
- A formulary lists covered drugs, and tiers set different cost sharing. Compare premium, deductible, pharmacy terms, exact medicines, and approvals.
- A low premium can still produce a higher total cost. Apply every stated need to the same current plan.
Which Gotchas Trip Students Up?
- Medicare Advantage is an alternative route for Medicare benefits; Medigap supplements Original Medicare.
- The word hospital does not make every charge Part A. Admission status and the billed service both matter.
- Standardized Medigap benefits do not mean identical premiums, universal availability, or automatic acceptance.
- Part C and Part D are different. An Advantage plan may include Part D, but the specific plan decides.
One-Breath Recap
Original Medicare uses Part A for qualifying inpatient facility care and Part B for physician and outpatient services. Medicare Advantage, or Part C, delivers Medicare benefits through a private plan with plan-specific networks, approvals, costs, and possible drug coverage. Part D covers outpatient prescriptions. Medigap works only with Original Medicare, covers one person, and applies its stated benefit after Medicare pays. Same-letter Medigap policies have the same basic benefits where standardization applies, but premiums and availability can differ. Admission status, approved amounts, current plan documents, formularies, and enrollment rights answer separate questions.
Need more than the recap? Read the full Medicare and Medigap unit.