Medicare Part C and Part D are two different add-ons to Original Medicare

Medicare Part C (also called Medicare Advantage) is an alternative way to receive your Part A and Part B benefits through a private insurance company instead of Original Medicare. Medicare Part D is prescription drug coverage you add to Original Medicare or Part C. They are separate programs with different rules, costs, and coverage — and you do not have to choose both.

Part C replaces your Original Medicare entirely if you join. Part D is always an add-on: you can use it with Original Medicare, or it comes bundled into most Part C plans. Understanding which one you need depends on your prescription costs, your doctors, and how much you want to pay upfront.

Key Takeaways

  • Medicare Part C is sold by private insurers and covers hospital, medical, and usually prescription drug benefits in one plan, replacing Original Medicare.
  • Medicare Part D is prescription drug coverage only, and you add it to Original Medicare or get it as part of a Part C plan.
  • Part C plans often have lower monthly premiums than Original Medicare but may require you to use in-network doctors and hospitals.
  • Part D plans vary widely in which drugs they cover and what you pay, so comparing plans each year can save you hundreds of dollars on prescriptions.
  • You can switch between Part C and Original Medicare during the annual enrollment period (October 15 to December 7), but missing the important date means waiting until the next year.

How Medicare Part C works and who sells it

Medicare Part C is offered by private insurance companies — UnitedHealthcare, Humana, Aetna, Cigna, and others — that contract with Medicare. When you join a Part C plan, you give up Original Medicare (Part A and Part B) and the private insurer becomes responsible for covering your hospital stays, doctor visits, and other medical care. You still pay the Part B premium to Medicare, but you also pay the Part C plan's monthly premium to the private company.

Most Part C plans include prescription drug coverage (Part D) built in, so you do not buy them separately. Some plans also cover dental, vision, or hearing — benefits Original Medicare does not pay for. However, Part C plans almost always require you to use doctors and hospitals in their network. If you see an out-of-network provider, you pay more or the plan may not cover it at all. This is the main trade-off: lower premiums and extra benefits in exchange for less freedom to choose your providers.

How Medicare Part D works and what it covers

Medicare Part D is prescription drug coverage only. If you have Original Medicare, you buy Part D from a private insurer (the same companies that sell Part C). If you have Part C, the drug coverage is usually included. Part D plans vary significantly in which drugs they cover, how much you pay for each drug, and which pharmacies you can use.

Each Part D plan has a formulary — a list of covered drugs organized by tier. Drugs on lower tiers (usually generic medications) cost you less. Drugs on higher tiers or not on the formulary at all cost you more or may not be covered. If your doctor prescribes a drug that is not on your plan's formulary, you can ask the plan to cover it anyway (called an exception), but this takes time and is not always approved.

Part D has a coverage gap called the "donut hole." Once you and your plan spend a combined $5,850 on covered drugs in 2024 (this amount changes yearly), you enter the gap and pay a higher percentage of drug costs until your out-of-pocket spending reaches $7,050. After that, catastrophic coverage kicks in and you pay a small copay for the rest of the year. The exact amounts shift annually, so check your plan's details each year.

Costs: premiums, deductibles, and copays

Part C premiums vary by plan and location. Some plans have no monthly premium beyond what you pay Medicare for Part B, while others charge $50 to $200 or more per month. Part C plans also have deductibles and copays for doctor visits and hospital stays, similar to commercial health insurance. The total cost depends on how much medical care you use.

Part D premiums also vary by plan, typically ranging from $7 to $100 per month, though this changes yearly. Part D has a deductible (usually $0 to $550 in 2024) before the plan starts paying for drugs. After you meet the deductible, you pay a copay or coinsurance for each prescription. Once you hit the donut hole, your costs jump significantly until catastrophic coverage begins.

Original Medicare (Part A and Part B) has its own costs: a Part B premium (currently $164.90 per month for most people in 2024, but this changes yearly), a Part A deductible for hospital stays, and coinsurance for longer hospital stays. If you add Part D to Original Medicare, you pay the Part D premium on top. Comparing the total cost of Part C versus Original Medicare plus Part D requires looking at your specific situation: your prescription costs, your expected doctor visits, and which doctors you want to see.

When you can join or switch between Part C and Part D

You can join Part C or Part D when you first become may be able to access for Medicare (usually at age 65). If you miss that window, you can join during the Annual Enrollment Period, which runs from October 15 to December 7 each year. Coverage begins January 1 of the following year.

If you are already in Original Medicare and want to switch to Part C, you can do so during the Annual Enrollment Period. If you are in Part C and want to switch back to Original Medicare, you can also do so during this period. However, if you drop Part D coverage and do not join another plan within 63 days, you may face a permanent late-enrollment penalty on any Part D plan you join later. The penalty is roughly 1% of the national average Part D premium for each month you were without coverage.

There is also a Part C disenrollment period from January 1 to February 14 each year, during which you can switch to a different Part C plan or return to Original Medicare without penalty. Outside these windows, you are locked into your current plan until the next Annual Enrollment Period.

Part C network restrictions versus Original Medicare flexibility

The biggest practical difference between Part C and Original Medicare is choice of providers. Original Medicare works with any doctor or hospital that accepts Medicare, anywhere in the country. Part C plans have networks: you must use in-network providers for full coverage, and out-of-network care is either not covered or costs significantly more.

If you have a doctor you want to keep seeing, check whether they are in your Part C plan's network before you join. If your doctor is not in the network and will not join, staying with Original Medicare may be worth the higher premium. Conversely, if you are willing to switch doctors or your current doctors are in the network, Part C can save you money.

Part C plans also typically require you to get a referral from your primary care doctor before seeing a specialist, whereas Original Medicare does not. This adds a step but can help coordinate your care. Emergency care and urgent care are usually covered in-network and out-of-network under Part C, but it is worth confirming with your specific plan.

How to compare Part C and Part D plans

Medicare publishes a plan comparison tool at Medicare.gov where you can enter your zip code, your current doctors, and your prescriptions to see which plans cover them and what you would pay. This tool shows you the monthly premium, deductible, copays, and whether your doctors are in-network for each Part C plan. For Part D, it shows you the premium, deductible, and what you would pay for each of your current drugs.

Comparing plans every year is important because formularies change, networks change, and premiums change. A plan that was cheapest last year may not be this year. Many people find that switching plans saves them $500 to $1,500 per year, especially if their prescriptions have changed or if a new generic version of a drug they take has become available.

You can also call 1-800-MEDICARE to speak with someone who can walk you through plan options, or contact your State Health Insurance information Program (SHIP), which offers free counseling. SHIP can be found through your state's aging office or at shiptalk.org.

Frequently Asked Questions

Can I have both Part C and Original Medicare at the same time?

No. Part C replaces Original Medicare entirely. If you join Part C, you are no longer enrolled in Part A and Part B. If you later switch back to Original Medicare, you must rejoin Part D separately if you want prescription drug coverage, or you may face a late-enrollment penalty.

What happens to my Part D coverage if I switch from Part C to Original Medicare?

Part D coverage ends when you leave Part C. You must join a standalone Part D plan during the Annual Enrollment Period or within 63 days of losing Part C coverage to avoid a permanent late-enrollment penalty. If you miss this window, the penalty applies to any Part D plan you join later.

Do Part C plans cover everything Original Medicare covers?

Part C plans must cover at least everything Original Medicare covers (hospital, medical, and prescription drugs), but they may have different copays, deductibles, and network restrictions. Some Part C plans cover additional services like dental or vision. Read your plan's coverage details to understand what is included.

Can my doctor refuse to accept my Part C plan?

Doctors can choose not to join a Part C network. If your doctor is not in your plan's network, you can still see them, but you will pay out-of-network rates or the plan may not cover the visit. Before joining a Part C plan, confirm that your doctors are in-network or are willing to join.

What if my Part D plan stops covering a drug I need?

You can ask your plan for an exception to cover the drug anyway, or you can ask your doctor to prescribe a similar drug that is on the formulary. If the plan denies your exception, you can appeal. You can also switch to a different Part D plan during the Annual Enrollment Period if your current plan no longer meets your needs.