When is open enrollment for Medicare, and which of the three windows actually applies to your situation?
Most people mean the fall Annual Enrollment Period when they ask this question. But there are two other windows that matter just as much depending on what you are trying to change.
This guide walks through all three, what each one actually allows, and a simple timeline to work from this fall.
The Three Windows People Confuse as One
Medicare actually runs on three separate enrollment calendars, not one.
The Annual Enrollment Period in the fall gets the most attention. But the Medicare Advantage Open Enrollment Period in the new year and the MediGap enrollment window tied to your own Part B start date each open different doors. Knowing which window you are in changes what you are allowed to do.
Here is what each one covers.
AEP: October 15 Through December 7
This is the window most people mean when they ask when is open enrollment for Medicare.
During the Annual Enrollment Period, you can switch from Original Medicare to a Medicare Advantage plan, switch back to Original Medicare, move between Medicare Advantage plans, or join, switch, or drop a Part D prescription drug plan. Every change made during AEP takes effect January 1.
It is the one window every Medicare beneficiary should mark every year, whether or not you plan to change anything.
Medicare Advantage Open Enrollment: January 1 Through March 31
This second window only applies if you are already in a Medicare Advantage plan.
If your AEP choice is not working out, this window gives you one more change. You can switch Medicare Advantage plans, or return to Original Medicare and add a Part D plan. You only get one change, so use it deliberately.
It is a safety net, not a second AEP.
The Medigap Enrollment Window: Six Months From Part B
The third window is the one that gets the least attention and matters the most.
Your Medigap, or Medicare supplement, enrollment window runs for six months starting the first day of the month you are both 65 or older and enrolled in Medicare Part B.
During this window, insurers must sell you any Medigap plan offered in your state at the best available rate, regardless of your health history. Miss it, and most insurers can require medical underwriting or decline your application outright.
Unlike AEP, this window does not repeat every year. It happens once, tied to your own Part B start date.
What You Can Actually Change in Each Window
- Annual Enrollment Period: move between Medicare Advantage and Original Medicare, switch Medicare Advantage plans, and join, switch, or drop a Part D plan.
- Medicare Advantage Open Enrollment: make one plan switch or one return to Original Medicare, if you are already in a Medicare Advantage plan.
- Your personal MediGap window: enroll in any MediGap plan sold in your state without medical underwriting.
Outside of these three windows, changes generally require a Special Enrollment Period tied to a specific qualifying event.
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What You Cannot Change Outside These Windows
It helps to be just as clear about what these windows do not let you do.
Once your personal MediGap window closes, switching MediGap plans usually means medical underwriting. Once you use your one Medicare Advantage switch between January and March, you cannot make a second. Special Enrollment Periods cover a few events, such as a move or losing employer insurance, but they are the exception.
That is exactly why reviewing your plan every AEP matters, even if nothing about your health has changed.
A Simple Timeline for Fall 2026
Here is how the fall actually unfolds if you want to review your plan.
- Late September: Your current Medicare Advantage or Part D plan sends an Annual Notice of Change listing every adjustment to premium, deductible, drug list, and benefits for next year.
- October 15 to December 7: The Annual Enrollment Period opens, and any change you make takes effect January 1.
- January 1 to March 31: If your AEP choice is not working, the Medicare Advantage Open Enrollment Period gives you one more chance to adjust.
Reading the Annual Notice of Change beside your current plan documents, rather than on its own, is the single habit that makes AEP easy instead of overwhelming.
Why Reviewing Matters More for 2027
Every AEP is worth a review, but 2027 carries a bit more weight than a typical year.
Plans can shift in premium, drug formulary, or network from one plan year to the next. Your Annual Notice of Change is built to flag exactly those shifts. If you have not opened it yet, pull it out before you decide anything.
A ten-minute comparison against your current plan is usually enough to know whether it is worth a longer look.
A Simple Way to Remember Which Window Applies
When someone asks when is open enrollment for Medicare, the honest answer depends on which situation they are actually in.
- If you are choosing a plan for the first time or reviewing everything at once, you want AEP, October 15 through December 7.
- If you already picked a Medicare Advantage plan during AEP and it is not working out, you want the Medicare Advantage Open Enrollment Period, January 1 through March 31.
- If you are newly eligible for Medicare and want a MediGap plan without medical underwriting, you want your own personal six-month window tied to your Part B start date.
Matching your situation to the right window is most of the battle.
What You Cannot Change Outside These Windows
It helps to be just as clear about what these windows do not let you do.
You generally cannot switch Medigap plans without medical underwriting once your personal enrollment window has closed, and you cannot make a second Medicare Advantage change once you have used your one switch during January through March. A handful of Special Enrollment Periods exist for specific situations, such as moving out of a plan’s service area or losing other coverage, but they are the exception, not a standing option.
That is exactly why reviewing your plan every AEP matters, even if nothing about your health has changed.
A Simple Timeline for Fall 2026
Here is how the fall actually unfolds if you want to review your plan.
- Late September: Your current Medicare Advantage or Part D plan sends an Annual Notice of Change listing every adjustment to premium, deductible, drug list, and benefits for next year.
- October 15 to December 7: The Annual Enrollment Period opens, and any change you make takes effect January 1.
- January 1 to March 31: If your AEP choice is not working, the Medicare Advantage Open Enrollment Period gives you one more chance to adjust.
Reading the Annual Notice of Change beside your current plan documents, rather than on its own, is the single habit that makes AEP easy instead of overwhelming.
Why Reviewing Matters More for 2027
Every AEP is worth a review, but 2027 carries a bit more weight than a typical year.
Plans that felt like a good fit last year can shift meaningfully in premium, drug formulary, or network from one plan year to the next, and those changes are exactly what the Annual Notice of Change is built to flag. If you have not opened that notice yet, it is worth pulling out before you decide anything.
A ten-minute comparison against your current plan is usually enough to know whether it is worth a longer look.
A Simple Way to Remember Which Window Applies
When someone asks when is open enrollment for Medicare, the honest answer depends on which situation they are actually in.
- If you are choosing a plan for the first time or reviewing everything at once, you want AEP, October 15 through December 7.
- If you already picked a Medicare Advantage plan during AEP and it is not working out, you want the Medicare Advantage Open Enrollment Period, January 1 through March 31.
- If you are newly eligible for Medicare and want a MediGap plan without medical underwriting, you want your own personal six-month window tied to your Part B start date.
Matching your situation to the right window is most of the battle.
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Frequently Asked Questions
Q: When is open enrollment for Medicare each year?
A: The Annual Enrollment Period runs October 15 through December 7 every year, and any change you make takes effect January 1. This is the window most people mean when they ask about Medicare open enrollment.
Q: Is Medicare Advantage Open Enrollment the same as AEP?
A: No.
Medicare Advantage Open Enrollment runs January 1 through March 31 and only applies if you are already enrolled in a Medicare Advantage plan. It allows one additional switch, not the full menu of changes available during AEP.
Q: When does my personal Medigap enrollment window open?
A: It opens the first day of the month you are both 65 or older and enrolled in Part B, and it lasts six months. During that window, insurers cannot use your health history to deny you a policy or charge you more.
Q: What happens if I miss all three windows?
A: You may still qualify for a Special Enrollment Period tied to a specific event, such as losing other coverage or moving. Outside of that, Medigap applications are typically subject to medical underwriting until your next opportunity.
Q: When does open enrollment for Medicare change from year to year?
A: The Annual Enrollment Period and the Medicare Advantage Open Enrollment Period are set by federal law and run the same dates every year: October 15 to December 7, and January 1 to March 31. Your own Medigap window is the only one tied to a personal date rather than the calendar year.
Q: Can I use Medi-Share 65+ instead of a Medigap plan?
A: Some Medicare-eligible members choose Medi-Share 65+, a health sharing option, to help with costs Original Medicare does not pay. It is not insurance and works differently from a Medigap plan, so it is worth comparing both before you decide which fits your situation.
Call me directly for a free, no-pressure review.
Leslie Alford, Personal Benefits Manager, MediGap Advisors
Direct Line: 720-943-6321
There is no cost and no obligation.
Leslie Alford is a Personal Benefits Manager at MediGap Advisors. Leslie has a passion for bringing clarity to those confused about Medicare. She is an authority on Medicare, Medicare supplement plans, Medicare Advantage plans, and Part D prescription drug plans. Read more about Leslie on her Bio page.