Yes, Medicare has both Part C and Part D — they are optional add-ons to Original Medicare
Part C (also called Medicare Advantage) is an alternative way to get your Part A and Part B coverage. Instead of using Original Medicare, you join a private insurance plan that contracts with Medicare. That plan handles your hospital and doctor visits.
Part D is prescription drug coverage. It is separate from Part C. You can add Part D to Original Medicare, or it often comes bundled into a Part C plan. Part D is not automatic — you have to choose it, and there is a penalty if you wait too long to sign up.
Neither part is required. You can stay on Original Medicare alone. But most people choose at least one because the out-of-pocket costs are lower than paying for everything yourself.
Key Takeaways
- Part C replaces Original Medicare with a private plan; Part D adds prescription drug coverage to either Original Medicare or Part C.
- Part C usually includes dental, vision, and hearing benefits that Original Medicare does not cover.
- Part D plans vary widely in which drugs they cover and how much you pay, so comparing plans each year matters.
- You can switch Part C or Part D plans once a year during the Annual Enrollment Period (October 15 to December 7).
- Delaying Part D enrollment when you first become may be able to access can result in a permanent penalty added to your premium.
How Part C (Medicare Advantage) differs from Original Medicare
Original Medicare is run by the federal government. You go to any doctor or hospital that accepts Medicare, and Medicare pays its share. Part C is run by private insurance companies — Humana, UnitedHealthcare, Aetna, and others. When you join a Part C plan, that company becomes your main insurance.
Most Part C plans are HMOs (Health Maintenance Organizations) or PPOs (Preferred Provider Organizations). An HMO requires you to use doctors and hospitals in its network, and you usually need a referral to see a specialist. A PPO lets you see any doctor but charges more if you go out of network. Some plans are regional; others cover the whole country.
Part C plans often include benefits Original Medicare does not: dental cleanings, eyeglasses, hearing aids, and fitness programs. They also have a yearly out-of-pocket maximum — once you hit it, the plan pays everything else for the rest of that year. Original Medicare has no maximum.
The trade-off is that Part C plans have networks, referral requirements, and prior authorization rules. If you like your current doctor, you need to check whether they are in the plan's network before you join.
How Part D (prescription drug coverage) works
Part D is coverage for prescription medications only. It does not cover doctor visits or hospital stays. You buy it from a private insurance company, just like Part C, but it is a separate product.
Part D plans differ in which drugs they cover (called the formulary), how much you pay for each drug, and which pharmacies you can use. A drug that costs $10 a month on one plan might cost $50 on another, or might not be covered at all. This is why comparing plans each year is important — your best plan can change.
You pay a monthly premium for Part D. You also pay out of pocket when you fill a prescription: a copay or coinsurance for each drug. Once your total drug costs hit a certain amount in a year, you enter the "coverage gap" (also called the donut hole), where you pay more. After you spend enough out of pocket, catastrophic coverage kicks in and the plan pays most of the cost.
Part D is optional, but there is a cost to waiting. If you do not sign up when you first become may be able to access for Medicare and you do not have other creditable drug coverage, you pay a penalty for every month you were not enrolled. That penalty is added to your Part D premium permanently.
When you can enroll in Part C or Part D
Your first chance to join Part C or Part D is during your Initial Enrollment Period, which starts three months before the month you turn 65 and ends three months after. If you miss this window, you can still join, but you may face a penalty.
Every year, the Annual Enrollment Period runs from October 15 to December 7. During this time, you can switch Part C plans, switch Part D plans, drop Part C and go back to Original Medicare, or add Part D to Original Medicare. Changes take effect January 1.
There are also special enrollment periods if you move, lose coverage, or have a may have access to life event. These let you change plans outside the annual window.
Part C and Part D costs and coverage limits
Part C premiums vary by plan and location. Some plans have no premium at all (you pay only the Part B premium to Medicare). Others charge $50 to $200 or more per month. Plans with lower premiums often have higher deductibles or copays.
Part D premiums also vary. Basic plans might cost $5 to $15 a month; more comprehensive plans cost $30 to $100 or more. The premium you pay depends on the plan you choose and where you live.
Part C plans have an out-of-pocket maximum. In 2024, that maximum ranges from about $4,500 to $10,000 per year, depending on the plan. Once you reach it, the plan pays 100% of covered services for the rest of the year. Original Medicare has no maximum.
Part D has a different structure. You pay your share of drug costs until your total spending (your copays plus what the plan pays) reaches a threshold. Then you enter the coverage gap. After you spend enough out of pocket, catastrophic coverage begins and you pay only a small copay or coinsurance.
Common mistakes when choosing Part C or Part D
The biggest mistake is not comparing plans every year. Even if you were happy with your plan last year, the drugs it covers, the doctors in its network, and the premiums can all change. Spending an hour comparing plans during the Annual Enrollment Period can save you hundreds of dollars.
Another common error is delaying Part D enrollment. The penalty for late enrollment is 1% of the national average Part D premium for each month you were not enrolled. If you wait two years, that penalty is permanent — it stays on your premium for life. There is no catch-up period.
People also sometimes assume their doctor is in a Part C plan's network without checking. Always verify before you enroll. Call the plan, use its website, or ask your doctor's office directly.
Finally, some people choose a plan based on premium alone and ignore the deductible, copays, and out-of-pocket maximum. A plan with a low premium might have high copays that cost you more overall if you use a lot of services.
How to find and compare Part C and Part D plans
Medicare.gov has a plan finder tool where you enter your location, current doctors, and medications. It shows you all available Part C and Part D plans, their premiums, deductibles, copays, and which drugs and doctors they cover. You can compare side by side.
You can also call 1-800-MEDICARE to speak with someone who can walk you through your options. Many local Area Agencies on Aging offer free counseling on Medicare plans as well.
When you compare, write down the plans you are considering and their key details: the monthly premium, the deductible, the copays for your regular medications and doctor visits, and the out-of-pocket maximum. Then add up what you think you will spend in a year on each plan. The cheapest premium is not always the cheapest plan overall.
Frequently Asked Questions
Can I have both Part C and Part D at the same time?
Most Part C plans include Part D coverage, so you get both in one plan. If you choose Original Medicare instead of Part C, you can add a standalone Part D plan. You cannot have two Part D plans at once, but you can switch plans during the Annual Enrollment Period.
What happens if I do not choose Part C or Part D?
You stay on Original Medicare. You pay the Part B premium and your share of costs when you use services. You will not have prescription drug coverage unless you add Part D. If you delay Part D, you will owe a penalty later.
Can I switch from Part C back to Original Medicare?
Yes, during the Annual Enrollment Period (October 15 to December 7) you can drop your Part C plan and return to Original Medicare. The change takes effect January 1. You can also switch if you move or have a may have access to life event.
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 rules. They may require prior authorization, use a network, or charge different copays. Read the plan's coverage details before you join.
What if my medication is not on my Part D plan's formulary?
You can ask the plan for an exception, which sometimes is approved. You can also switch to a different Part D plan during the Annual Enrollment Period that does cover the drug. Talk to your doctor about whether a covered alternative medication would work for you.