Start with the two coverage paths
Original Medicare consists of Parts A and B. You can add a separate Part D plan and may add Medigap or another qualifying source of supplemental coverage. Medicare Advantage is an alternative way to receive Medicare benefits through a Medicare-approved private plan.
Medicare.gov's explanation of the parts is the authoritative starting point. The letters describe different roles, not a sequence in which everyone buys A, B, C and D as four independent policies.
| Name | Main role | Common misunderstanding |
|---|---|---|
| Part A | Hospital insurance and specified related services | It does not mean every care expense is fully paid |
| Part B | Medical and outpatient coverage | It is not automatically free because Part A may be premium-free |
| Part C | Medicare Advantage delivery through a private plan | It is not a supplement that pays Original Medicare's bills |
| Part D | Prescription drug coverage | Plans do not all cover every drug on identical terms |
| Medigap | Helps with specified Original Medicare cost sharing | It does not pay Medicare Advantage copays |
Part A: hospital insurance with conditions
Part A helps cover inpatient hospital care, qualifying skilled nursing facility care, hospice and certain home health services. Each category has eligibility and coverage conditions. The word hospital does not establish that every charge during a visit falls under Part A.
Many people qualify for premium-free Part A based on work history, but premiums are only one cost. Deductibles, coinsurance and coverage limits can still apply. Check the current official costs for the year you need coverage rather than relying on a figure from an old article.
If an expected service is important to your planning, use Medicare's coverage resources and ask the provider how it is classified. This article explains the insurance structure, not whether a particular treatment is medically appropriate or covered in your situation.
Part B: medical and outpatient services
Part B helps cover services from clinicians, outpatient care, durable medical equipment and many preventive services, subject to Medicare rules. It generally has a monthly premium and cost sharing for covered services.
Under Original Medicare, provider participation and assignment can affect practical access and charges. Confirm that a provider takes Medicare and ask about the service's coverage. Do not assume the ability to see a provider means every service that provider offers is covered.
Part B enrollment timing can matter even when you have another insurance card. Current-employment coverage, retiree coverage and COBRA are not interchangeable for enrollment purposes. Our enrollment checklist explains the distinction.
Part C: Medicare Advantage
To join Medicare Advantage, you generally need both Part A and Part B and must meet the plan's eligibility and service-area rules. You continue paying the Part B premium, along with any applicable plan premium.
Plans may use provider networks, referrals or prior authorization and have their own cost-sharing schedules. They have an annual limit on covered Part A and Part B out-of-pocket costs, but that is not a single cap covering all premiums, drugs and noncovered services.
Many plans include drug coverage and additional benefits such as certain dental, hearing or vision services. Those benefits can have networks, allowances and limits. A zero-dollar additional plan premium does not mean all care is free.
Use our Original Medicare versus Medicare Advantage comparison to evaluate the full arrangement without assuming either path is universally better.
Part D: compare the actual medication list
Part D is offered through private Medicare-approved plans, either separately with Original Medicare or within many Medicare Advantage plans. Formularies, pharmacy networks and cost-sharing rules differ.
Check the exact medications, doses, quantities and pharmacies you use. A low premium can be offset by higher drug costs or restrictions. Our Part D comparison guide provides a practical process.
If you have other drug coverage, ask whether it is creditable and keep the annual notice. Medicare.gov explains that a gap of 63 days or more without Medicare drug coverage or other creditable coverage can lead to a late-enrollment penalty when you enroll later. Discount cards are not drug insurance.
Medigap fills a different role
Medigap is private insurance that helps pay specified cost sharing in Original Medicare. It does not replace Parts A and B and cannot be used to pay Medicare Advantage cost sharing.
In most states, standardized plan letters describe the benefits. A Medigap Plan D is not Medicare Part D, and Medigap Plan G is not another Medicare part. Massachusetts, Minnesota and Wisconsin use different standardization systems.
Timing matters because the federal Medigap open-enrollment period is a one-time six-month period when you are at least 65 and first enrolled in Part B. Later access can depend on guaranteed-issue rights, underwriting or state protections. Our Medigap comparison explains why that deserves attention before choosing a path.
Compare total cost and access together
For Original Medicare, consider Part B, any Part A premium, Part D, supplemental coverage and remaining cost sharing. For Medicare Advantage, consider Part B, any plan premium, medical and drug cost sharing, network access and additional-benefit limits.
Do not compare one path's premium with the other's total cost. Also account for travel and whether important providers participate. Original Medicare without supplemental protection has no general annual Part A and Part B out-of-pocket ceiling, while Medicare Advantage's limit has defined scope.
Medicare.gov's coverage-options page links to free State Health Insurance Assistance Program counseling. SHIP can help explain choices without being an insurance company or plan.
Frequently asked questions
Do I need all four parts?
Not as four separate purchases. Parts A and B form the foundation, and you choose how to receive coverage and address drugs and remaining costs. Other coverage can affect the decision.
Is Medicare the same as Medicaid?
No. They are different programs with different eligibility and roles. Some people qualify for both, and coordination should be reviewed individually.
Does Medicare Advantage replace the need for Part B?
No. You generally must have both A and B to join and continue paying the Part B premium. Any plan-specific premium reduction has its own terms.
Can I add Medigap to Medicare Advantage?
Medigap is designed for Original Medicare and does not pay Advantage cost sharing. Investigate enrollment and Medigap purchase rights before changing paths.
Sources and methodology
This article uses public policy guidance and official product information, checked October 30, 2026. Insurance coverage and availability depend on the issued contract, state and personal eligibility. We did not apply for coverage, test a carrier or evaluate an actual claim for this article.