How to Enroll in Medicare Part C (Medicare Advantage)

What Medicare Part C Is and How to Join

Medicare Part C, also called Medicare Advantage, is an alternative way to get your Medicare coverage. Instead of using Original Medicare (Part A and Part B), you join a private insurance plan that contracts with Medicare. That plan becomes responsible for covering your hospital care, doctor visits, and other services that Original Medicare covers.

You can join a Medicare Advantage plan during specific times of the year. The main enrollment window is October 15 through December 7 each year, and coverage starts January 1. If you miss that window, you may still join during the General Enrollment Period (January 1 through March 31), though your coverage would not start until the following month. Some people also have special enrollment periods that let them join outside these windows if they have had a major life change.

To join, you contact the insurance company directly — by phone, online, or in person — and complete their enrollment process. You do not go through Medicare itself to enroll in Part C; you go through the plan you choose.

Key Takeaways

Medicare Advantage plans are run by private insurance companies and cover the same services as Original Medicare, often with added benefits like dental or vision.
You can join during the Annual Enrollment Period (October 15 through December 7) for coverage starting January 1, or during General Enrollment (January 1 through March 31) for coverage starting the following month.
You must have Medicare Part A and Part B already in place before you can join a Medicare Advantage plan.
Each plan has its own network of doctors and hospitals, so you should check whether your current doctors are in the plan's network before you join.
You can switch plans or return to Original Medicare once per year during the Annual Enrollment Period.

Who Can Join a Medicare Advantage Plan

You must be enrolled in both Medicare Part A (hospital insurance) and Medicare Part B (medical insurance) before you can join a Medicare Advantage plan. You must also live in the plan's service area — most plans cover a specific county or group of counties, not the entire country.

You cannot have End-Stage Renal Disease (ESRD), with limited exceptions. If you have ESRD, you may still be able to join certain plans, but you should contact Medicare directly at 1-800-MEDICARE to learn whether a plan will cover you.

If you have both Medicare and Medicaid (the state program for low-income people), you can join a Medicare Advantage plan, but some plans are designed specifically for dual-may be able to access people and may offer extra benefits.

The Three Enrollment Windows Each Year

Annual Enrollment Period (October 15 through December 7): This is the main window. Plans you join during this time start coverage on January 1. You can switch from Original Medicare to a Medicare Advantage plan, switch from one Medicare Advantage plan to another, or switch back to Original Medicare. This is the only time most people can make changes.

General Enrollment Period (January 1 through March 31): If you miss the Annual Enrollment Period, you can still join a Medicare Advantage plan here, but coverage does not start until the first day of the month after you join. For example, if you join on February 15, your coverage starts March 1. You cannot use this period to switch between Medicare Advantage plans or return to Original Medicare — only to join a plan for the first time during the calendar year.

Special Enrollment Periods: You may be able to join outside the regular windows if you have had a may have access to event, such as moving out of your plan's service area, losing other health coverage, getting married, or having a change in your Medicaid status. These periods last 60 days from the date of the event. Contact Medicare at 1-800-MEDICARE to find out whether your situation qualifies.

How to Compare Plans and Choose One

Medicare publishes a plan comparison tool on Medicare.gov where you can enter your zip code and see all the Medicare Advantage plans available in your area. The tool shows you the monthly premium, deductible, copays, and coinsurance for each plan, as well as which doctors and hospitals are in the network.

Before you choose, check three things: whether your current doctors and hospitals are in the plan's network, what the out-of-pocket costs are (premium, deductible, copays), and what extra benefits the plan offers beyond what Original Medicare covers. Many Medicare Advantage plans include dental, vision, hearing, or fitness benefits that Original Medicare does not.

If your doctor is not in the network, you can still see them, but you will pay more out of pocket. Some plans allow out-of-network care for emergencies or urgent care; others do not. Read the plan's Summary of Benefits document to understand what you will owe if you see an out-of-network provider.

Steps to Enroll Once You Have Chosen a Plan

Contact the insurance company that runs the plan you want to join. You can find their phone number on Medicare.gov or on the plan's website. Have your Medicare card handy when you call.

Tell the representative you want to join the plan and provide your name, date of birth, and Medicare number. The representative will confirm that you are may be able to access, that you live in the service area, and that you have Part A and Part B. They will also ask about any other health coverage you have, such as coverage through a spouse's employer.

You will receive a confirmation letter in the mail within 10 business days. Keep this letter — it shows your effective date and plan details. Your new plan will send you an insurance card before your coverage starts.

What Happens to Your Original Medicare When You Join Part C

When your Medicare Advantage plan coverage starts, your Original Medicare (Part A and Part B) does not end, but you stop using it. You will use your new plan's insurance card instead. You keep your Medicare card for your records, but you do not present it to doctors or hospitals.

If you have a Medigap policy (supplemental insurance that works with Original Medicare), you should contact that insurance company and ask them to cancel it. You cannot use both Medigap and Medicare Advantage at the same time, and paying premiums for both is a waste of money. Some insurance companies will cancel automatically when they learn you have joined a Medicare Advantage plan, but you should not rely on that — call and confirm.

If you have a Part D prescription drug plan, you can keep it while you have Medicare Advantage, but many Medicare Advantage plans include prescription drug coverage already. Check your new plan's drug formulary (the list of covered medications) to see whether your current medications are covered. If not, you may want to switch to a different plan or to a different Part D plan.

Changing Your Mind or Switching Plans Later

You have a 14-day window after your Medicare Advantage plan coverage starts to change your mind and return to Original Medicare. This is called the disenrollment period. Contact your new plan or call Medicare at 1-800-MEDICARE to cancel. Your coverage will end and Original Medicare will restart on the first day of the following month.

After that 14-day window closes, you can only switch plans or return to Original Medicare during the Annual Enrollment Period (October 15 through December 7). If you want to make a change at any other time, you will need a may have access to event that opens a Special Enrollment Period.

If you return to Original Medicare after being in a Medicare Advantage plan, you may want to enroll in a Medigap policy to cover costs that Original Medicare does not pay. You have a may provide issue right for Medigap for 63 days after you leave Medicare Advantage, which means insurance companies cannot deny you or charge you more based on your health. After that window closes, they can.

Frequently Asked Questions

Do I have to join a Medicare Advantage plan, or can I stay on Original Medicare?

You do not have to join. Original Medicare is available to everyone with Part A and Part B. Medicare Advantage is optional. Some people prefer Original Medicare because it works nationwide and does not use networks. Others prefer Medicare Advantage because of the extra benefits or lower out-of-pocket costs. Both are valid choices.

What if my doctor leaves the plan's network after I join?

If your doctor leaves the network, the plan must notify you and give you the option to continue seeing that doctor for a limited time while you transition to a new one. You can also switch to a different Medicare Advantage plan during a Special Enrollment Period. Contact your plan to learn your options.

Can I join a Medicare Advantage plan if I am still working and have employer health insurance?

Yes, but you should understand how the two plans will work together. Usually your employer plan is primary (pays first) and Medicare Advantage is secondary. Talk to your employer's benefits department and to the Medicare Advantage plan before you join to understand your costs and coverage.

What happens to my prescriptions if I switch from one Medicare Advantage plan to another?

Each plan has its own drug formulary. If your new plan does not cover a medication your old plan did, you may need to ask your doctor for a different medication or request an exception from the new plan. Contact the new plan's pharmacy department before your coverage starts to confirm your medications are covered.

Is there a penalty for joining Medicare Advantage late?

There is no late enrollment penalty for Medicare Advantage itself. However, if you delay joining any form of Medicare coverage when you are first may be able to access, you may face a penalty when you do join. If you have questions about your specific situation, contact Medicare at 1-800-MEDICARE.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.