Every fall, Medicare runs its Annual Enrollment Period (AEP) — a limited window when you can make important changes to your coverage. Missing this window means you're locked into your current plan for another full year, even if your drugs are no longer covered or your premiums have increased.
This guide tells you exactly what the dates are, what you can change, and — most importantly — a step-by-step checklist so you don't leave money on the table.
Annual Enrollment Period: October 15 – December 7, 2026
Changes take effect: January 1, 2027
Medicare Advantage OEP: January 1 – March 31 (limited changes only)
What You Can Change During AEP
During the Annual Enrollment Period, you can make any of these changes — and they all take effect January 1:
- Switch from Original Medicare to a Medicare Advantage plan
- Switch from Medicare Advantage back to Original Medicare
- Switch from one Medicare Advantage plan to a different one
- Join a Medicare Part D drug plan (if you don't have one)
- Switch from one Part D plan to a different one
- Drop your Part D plan entirely
You cannot use AEP to enroll in a Medigap (Medicare Supplement) plan. Medigap has its own separate enrollment rules tied to when you turn 65. Switching from Advantage back to Original Medicare during AEP may leave you unable to get Medigap coverage in many states.
Why You Must Review Every Single Year
Medicare plans are not static. Every January 1, your plan can legally change its premiums, its covered drug list (formulary), its network of doctors, its copays and coinsurance, and its prior authorization requirements. A plan that worked perfectly for you last year may cost you significantly more — or no longer cover your key medications — starting January.
Plans send Annual Notice of Change (ANOC) letters each September. Read yours carefully. If your drug moved to a higher tier or was dropped, that's your signal to shop.
Your AEP Action Checklist
- Gather your medication list: Write down every drug you take, the dosage, and how many times per day
- Read your ANOC letter: Arrives in September — look for changes to your drugs, premiums, or doctors
- Use Medicare Plan Finder: Go to medicare.gov, enter your drugs and pharmacy, compare ALL plans available in your zip code by total estimated annual cost
- Verify your doctors are still in network: If on Advantage, confirm your key doctors accept your new plan for next year
- Compare dental and vision benefits: If on Advantage, compare how plans' extra benefits changed
- Check Extra Help eligibility: If income is limited, apply before December 7 to have coverage January 1
- Make your change by December 7: Changes made October 15–December 7 all take effect January 1
What Happens After AEP — Medicare Advantage OEP
If you enrolled in a Medicare Advantage plan during AEP and then change your mind, you have one more chance: the Medicare Advantage Open Enrollment Period runs January 1–March 31. During this window, you can switch to a different MA plan or switch back to Original Medicare (and add Part D). You can only make one change during this period.
Get Free Help Comparing Plans
You don't have to do this alone. Every state has a free, unbiased Medicare counseling service called SHIP (State Health Insurance Assistance Program). SHIP counselors are not insurance agents — they have no financial incentive to recommend any plan — and they will sit with you and compare every plan available in your area based on your specific drugs and doctors.
Find your state's SHIP at shiphelp.org or call 1-800-MEDICARE.
Frequently Asked Questions
When is Medicare Annual Enrollment Period 2026?
Medicare Annual Enrollment Period (AEP) runs October 15 through December 7, 2026. Any changes made during this period take effect January 1, 2027. This is the main window when Medicare beneficiaries can switch plans, join a Part D plan, or change from Medicare Advantage to Original Medicare.
What can I change during Medicare Annual Enrollment Period?
During AEP you can switch from Original Medicare to Medicare Advantage, switch between Medicare Advantage plans, switch back to Original Medicare, join or switch Part D prescription drug plans, or drop Part D coverage. All changes take effect January 1 of the following year.
Do I have to do anything during Medicare Annual Enrollment?
You are not required to make changes, but you should review your plan every year. Medicare plans change their drug formularies, networks, premiums, and copays every January. Not reviewing can mean your medications are no longer covered or your costs have increased significantly without your knowledge.
How do I compare Medicare plans during Annual Enrollment?
Use Medicare's free Plan Finder at medicare.gov. Enter your medications, dosages, and preferred pharmacy to compare all Part D and Medicare Advantage plans available in your zip code. The tool calculates your estimated annual total cost for each plan — making comparison straightforward.
What is the Medicare Advantage Open Enrollment Period?
The Medicare Advantage Open Enrollment Period runs January 1 through March 31 each year. During this period, you can make one change — switching to a different MA plan or switching back to Original Medicare. You cannot use this period to join a plan if you are currently in Original Medicare.