Medicare’s letters describe different kinds of coverage. Parts A and B form Original Medicare. Part C means Medicare Advantage, an alternative way to receive Medicare benefits. Part D provides prescription coverage through a private Medicare-approved plan; it is not a recommendation for any particular treatment.
The parts at a glance
| Part | Main role | What to check |
|---|---|---|
| A | Hospital insurance, including qualifying inpatient, skilled nursing, hospice and some home health services. | Admission status, benefit requirements and hospital cost sharing. |
| B | Doctor and outpatient services, equipment and many preventive services. | Premium, deductible, provider participation and service-specific rules. |
| C | A private Medicare Advantage plan that provides A and B benefits, usually with Part D. | Network, authorization, total costs and optional additional benefits. |
| D | Separate or included prescription insurance. | The exact plan, covered benefits, costs and enrollment rules. |
Choose a coverage arrangement
With Original Medicare, you can use providers who take Medicare nationwide. You may add a separate Part D plan and, if eligible, Medigap or other supplemental coverage to help with covered expenses.
With Medicare Advantage, you must have both A and B and live in the plan’s service area. The plan may use networks and prior authorization. You continue paying the Part B premium unless assistance or a benefit covers it. Medigap cannot pay Medicare Advantage cost sharing.
Medigap letters are a different system
Medigap Plan A is not Medicare Part A, and Medigap Plan D is not Part D. Medigap policies supplement Original Medicare costs. Massachusetts, Minnesota and Wisconsin standardize these policies differently from most states.
Three things to confirm before enrolling
- Check your Medicare start dates and current employer or other coverage before making changes.
- Compare annual premiums, deductibles and likely costs, not just a monthly advertised price.
- Verify your doctors, hospitals and needed services using the exact plan and current documents.
Eligibility and enrollment windows differ by coverage type. A plan quote is not an enrollment confirmation, and a low premium does not mean every service is without cost. Keep the approved effective date and benefit documents together.
Related coverage questions
- Medicare Part A and Part B: What Each Covers
- Medicare Part B: Medical Coverage, Costs and Enrollment
- Medicare Premiums and Deductibles: 2026 Medical Costs