Part C and Part D are two different add-ons to Original Medicare that cover what the basic plan does not

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. Part D is prescription drug coverage that you add to Original Medicare (or that comes built into Part C plans). They are separate programs with different costs, coverage rules, and networks.

You do not have to choose either one. If you stay with Original Medicare, you keep your current coverage and can add Part D separately if you want drug coverage. If you choose Part C, you are switching away from Original Medicare entirely, and most Part C plans include drug coverage as part of the package.

Key Takeaways

  • Part C (Medicare Advantage) is a private insurance alternative to Original Medicare that usually includes drug coverage, dental, vision, and hearing benefits that Original Medicare does not cover.
  • Part D is prescription drug coverage only, and you add it to Original Medicare if you want it; it is separate from Part C.
  • Part C plans have networks (you usually pay less if you use doctors in the plan's network), while Original Medicare has no network restrictions.
  • Part D plans vary widely in which drugs they cover and how much you pay, so comparing plans each year is important because coverage changes.
  • You can switch between Part C and Original Medicare, or change your Part D plan, during the annual enrollment period from October 15 to December 7.

How Part C (Medicare Advantage) Works

Part C plans are run by private insurance companies that contract with Medicare. When you enroll in a Part C plan, you are still covered by Medicare, but the insurance company manages your benefits instead of the government. You still pay your Part B premium to Medicare, and then you pay the Part C plan's premium (which may be zero, or may be $50 to $200+ per month depending on the plan).

Most Part C plans include prescription drug coverage, dental, vision, hearing aids, and fitness benefits — things Original Medicare does not pay for. However, you must use doctors and hospitals that are in the plan's network, except in emergencies. If you see an out-of-network provider, you will pay more or the plan may not cover it at all. Some plans are Health Maintenance Organizations (HMOs), which require you to pick a primary care doctor and get referrals to see specialists. Others are Preferred Provider Organizations (PPOs), which give you more flexibility to see specialists without a referral, though you still pay less in-network.

Part C plans have an out-of-pocket maximum — a yearly cap on what you pay for covered services. Once you reach that limit, the plan pays 100% of covered costs for the rest of the year. Original Medicare has no out-of-pocket maximum, which means your costs can be unlimited.

How Part D (Prescription Drug Coverage) Works

Part D is drug coverage only. You add it to Original Medicare if you want it. If you are already in a Part C plan, drug coverage is usually included, so you do not need to choose a separate Part D plan.

Part D plans are run by private insurance companies and vary significantly in which drugs they cover, how much you pay, and which pharmacies you can use. Each plan has a formulary — a list of covered drugs — and drugs are sorted into tiers. Tier 1 drugs (usually generics) cost the least. Tier 2 and 3 drugs (brand-name or newer medications) cost more. Some drugs may not be on the formulary at all, meaning the plan will not pay for them unless you ask for an exception.

Part D has a coverage structure with several stages. You pay a monthly premium, then a yearly deductible (which varies by plan, typically $0 to $550). After you meet the deductible, you pay a copay or coinsurance for each prescription. Once your total out-of-pocket spending reaches a certain amount (called the "initial coverage limit"), you enter the "donut hole" — a gap where you pay a higher percentage of drug costs. After you spend enough to exit the donut hole, catastrophic coverage kicks in and you pay a small copay for the rest of the year.

Part C vs. Original Medicare: What Changes

If you choose Part C, you are leaving Original Medicare. This means you no longer use Medicare-accepted doctors freely — you must use the plan's network. You cannot use your Medigap supplemental insurance (if you have one) because Part C plans are not compatible with Medigap. Your out-of-pocket costs may be lower because of the out-of-pocket maximum, but they could also be higher if you need care outside the network or if the plan's copays are steep.

Original Medicare has no network. You can see any doctor or hospital that accepts Medicare, anywhere in the country. You can buy a Medigap plan to cover costs that Original Medicare does not pay. However, Original Medicare does not cover dental, vision, hearing, or prescription drugs unless you add Part D separately. Your costs are unpredictable because there is no out-of-pocket maximum.

The choice depends on your health, your doctors, and your budget. People with chronic conditions who see many specialists often prefer Original Medicare's freedom. People who want predictable costs and extra benefits often prefer Part C.

Comparing and Choosing Part C and Part D Plans

Every year, insurance companies change their Part C and Part D plans — they add or drop drugs, change copays, change networks, and change premiums. This means the best plan for you one year may not be the best plan the next year. You should compare plans every year during the annual enrollment period.

To compare Part C plans, use the Medicare Plan Finder tool on Medicare.gov. You can enter your doctors and hospitals to see which plans include them in their network. You can also call 1-800-MEDICARE to speak with someone who can walk you through the plans available in your area.

To compare Part D plans, use the Medicare Plan Finder or the Prescription Drug Plan Finder on Medicare.gov. Enter the drugs you take, and the tool will show you which plans cover them, what tier they are on, and what your costs will be at different pharmacies. Costs can vary by hundreds of dollars per year between plans, so this comparison is worth doing.

If you do not have Part D coverage and you go without it for more than 63 days in a row, you may have to pay a permanent penalty when you do enroll — a higher premium for as long as you have Part D. The same penalty applies if you do not enroll in Part C by your important date. These penalties do not go away, so it is important to enroll on time or during the enrollment period.

When You Can Change Your Mind

The main time to change Part C or Part D plans is during the annual enrollment period, which runs from October 15 to December 7 each year. Changes take effect on January 1. During this period, you can switch from Part C to Original Medicare, from Original Medicare to Part C, or change your Part D plan.

There are also limited times outside the annual enrollment period when you can make changes. If you move to a new state or county, if your plan leaves Medicare, if you lose other health coverage, or if you experience certain life events, you may be able to change plans. These are called Special Enrollment Periods, and they usually last 60 days. If you think you may have access to, call 1-800-MEDICARE to confirm.

If you are in a Part C plan and you want to switch back to Original Medicare and add Medigap, you have limited time to do so without being denied coverage or charged more. The best time to buy Medigap is within six months of first enrolling in Part B, or within 63 days of leaving a Part C plan. Outside these windows, insurance companies can deny you or charge you a higher premium based on your health.

Costs: Premiums, Deductibles, and Out-of-Pocket Limits

Part C costs vary widely. You always pay your Part B premium to Medicare (currently $164.90 per month for most people in 2024, though this changes yearly). Then you pay the Part C plan's premium, which can range from $0 to $300+ per month depending on the plan and your location. Some plans also have a yearly deductible before coverage begins, and then copays for doctor visits, hospital stays, and prescriptions. Part C plans have an out-of-pocket maximum, typically $6,700 to $8,000 per year, meaning once you reach that amount, the plan pays 100% of covered costs.

Part D costs also vary. You pay a monthly premium (typically $5 to $100+ depending on the plan), a yearly deductible (typically $0 to $550), and then copays or coinsurance for each prescription. The total amount you spend on premiums, deductibles, copays, and coinsurance counts toward your out-of-pocket maximum, which is capped at around $7,050 per year. After you reach that limit, the plan pays 100% of your drug costs for the rest of the year.

If you are on a limited income, you may be able to get help paying Part C or Part D costs through programs like the Low-Income Subsidy (LIS) or Extra Help. These programs are run by Social Security and Medicare. To learn whether you may have access to, call 1-800-MEDICARE or visit Medicare.gov.

Frequently Asked Questions

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

Most Part C plans include Part D drug coverage, so you do not need a separate Part D plan. However, if your Part C plan does not include drugs, you can add a standalone Part D plan. You cannot be enrolled in two Part C plans or two Part D plans at the same time.

What happens if I do not enroll in Part D when I first become may be able to access?

If you go without Part D coverage for more than 63 days in a row after you first become may be able to access, you will owe a permanent late enrollment penalty. This penalty is added to your Part D premium for as long as you have Part D coverage. The penalty is about 1% of the national average Part D premium for each month you were without coverage, so delaying can cost you hundreds of dollars over time.

Can I switch from Part C back to Original Medicare anytime I want?

You can switch during the annual enrollment period (October 15 to December 7) or if you may have access to for a Special Enrollment Period due to a life event or move. Outside these windows, you are locked into your Part C plan until the next enrollment period. If you switch back to Original Medicare, you have 63 days to buy a Medigap plan without being denied or charged more based on your health.

Do Part C plans cover everything Original Medicare covers?

Part C plans must cover everything Part A and Part B cover, but they can have different copays, deductibles, and network restrictions. Some services may require prior authorization or may only be covered in-network. Always check the plan's coverage details before enrolling, especially if you have specific health needs.

How do I know if my doctor is in a Part C plan's network?

Use the Medicare Plan Finder on Medicare.gov and enter your doctor's name. The tool will show you which Part C plans include that doctor. You can also call the plan directly or visit the plan's website to check the provider directory. Networks change, so check again before you enroll and each year during enrollment period.