Medicare Annual Enrollment Period (AEP): Key Dates & What to Do
Medicare’s Annual Enrollment Period runs October 15 through December 7 every year. Here’s exactly what it’s for, what you can change, and what happens if you miss it.
By Boris Sorto, Healthcare Advocate · Updated August 26, 2026
Medicare’s Annual Enrollment Period (AEP) runs October 15 through December 7 every year. During this window, anyone with Medicare can switch Medicare Advantage plans, switch between Original Medicare and Medicare Advantage, join or drop a Part D drug plan, or switch Part D plans. Any change you make takes effect January 1 of the following year.
Key dates at a glance
AEP isn’t the only Medicare enrollment window. It’s just the one that applies to the most people, every year, without a qualifying event.
| Window | Dates | Who it’s for |
|---|---|---|
| Annual Enrollment Period (AEP) | Oct 15 – Dec 7 | Anyone with Medicare: switch MA, Part D, or Original Medicare |
| Medicare Advantage Open Enrollment (MA OEP) | Jan 1 – Mar 31 | Only those already in a Medicare Advantage plan |
| Initial Enrollment Period (IEP) | 7-month window around your 65th birthday | First-time enrollees. See our Turning 65 checklist |
| Special Enrollment Period (SEP) | Varies by qualifying event | Those who lost coverage, moved, or had another qualifying life event |
What you can do during AEP
- Switch from Original Medicare to a Medicare Advantage plan, or vice versa
- Switch from one Medicare Advantage plan to another
- Join a Part D prescription drug plan for the first time
- Switch from one Part D plan to another, or drop Part D coverage entirely
What happens if you miss it
If you miss AEP and you’re enrolled in Medicare Advantage, your next chance is the narrower MA OEP (January 1 – March 31), which only lets you change within Medicare Advantage or drop back to Original Medicare, not join Medicare Advantage for the first time. Outside of both windows, you generally need a qualifying life event to trigger a Special Enrollment Period, or you wait for the next AEP.
Reviewing your coverage before AEP starts, not during the last week, gives you time to actually act on what you find. See our Medicare Annual Checkup for a full review before the window opens.
Frequently asked questions
Can I switch Medicare Advantage plans outside of AEP?
Only during a separate window called the Medicare Advantage Open Enrollment Period (January 1 – March 31), and only if you’re already enrolled in a Medicare Advantage plan. You can switch to a different MA plan or drop back to Original Medicare, but you cannot switch from Original Medicare into an MA plan during that window.
Do I need to do anything during AEP if I’m happy with my current plan?
Not strictly, but it’s worth a quick review anyway, since plans commonly change their premiums, drug formularies, and provider networks each year, so a plan that fit well last year isn’t guaranteed to fit the same way next year.
When do AEP changes actually take effect?
January 1 of the following year, regardless of when during the October 15 – December 7 window you made the change.
Written by Boris Sorto
Bilingual Healthcare Advocate, formerly with Humana’s Medicare operations. More about Boris →