The Annual Enrollment Period: October 15 to December 7

The Annual Enrollment Period, often shortened to AEP, is the one Medicare window almost everyone has heard of. It runs from October 15 through December 7 every year, and it is the main opportunity for people on Medicare Advantage or Part D to review their coverage and make a change for the following year.

Who can use it

Unlike most other Medicare enrollment windows, AEP does not require a life event or a special circumstance to qualify. If you are enrolled in a Medicare Advantage plan or a stand-alone Part D prescription drug plan, you can use this window. It is simply an open period that occurs every year, available to anyone who wants to look at what else is available or make a change before the new plan year starts.

What you can do during AEP

During this window, you can switch from one Medicare Advantage plan to another, switch from one stand-alone Part D plan to another, join a Medicare Advantage plan for the first time if you are coming from Original Medicare, or drop a Medicare Advantage plan and return to Original Medicare. If you return to Original Medicare, you can also enroll in a stand-alone Part D plan at the same time. In short, this is the window where nearly any combination of changes to your Advantage or Part D coverage is possible, without needing to explain why.

Common reasons people use this window

There is no single reason people call during AEP, but a few come up often. A premium or deductible went up between one plan year and the next. A doctor or pharmacy that used to be in network is not anymore, since Advantage plans update their networks every year. A medication moved to a higher cost tier or dropped off the plan's formulary entirely. Or someone simply wants to confirm, once a year, that their current plan is still the right fit before letting it roll over automatically. None of these require anything more than wanting to look — that is the entire point of an open window.

Why the ANOC letter is the trigger for most people

Every Medicare Advantage and Part D plan is required to send its members an Annual Notice of Change, or ANOC, no later than September 30. That letter lays out what is different about your plan for the coming year — premium, deductible, copays, which pharmacies and doctors are in network, and which drugs are covered and at what tier. It arrives right before AEP opens, and it is usually what prompts people to check their options in the first place. Reading it side by side with your current costs and prescriptions is the only way to know whether anything meaningful has changed for you.

If you have not looked at yours yet, or you are not sure what it means, that is a good place to start. See what your ANOC letter is telling you.

What happens if you do nothing

If you do not make a change during AEP, your current Medicare Advantage or Part D enrollment generally continues into the new plan year, subject to whatever changes your plan made to its premium, benefits, or network — the same changes described in your ANOC letter. Doing nothing is a valid choice if your plan still works for you. The point of this window is to make sure that choice is an informed one, rather than one made by default.

When changes take effect

Any change you make during AEP — new plan, dropped plan, or a return to Original Medicare — takes effect on January 1 of the following year, regardless of whether you made the change on October 16 or December 6. If you miss this window, you will generally need to wait for the next AEP, unless you qualify for a different enrollment period based on your circumstances.

AEP versus the other enrollment windows

AEP is the broadest window, but it is not the only one. If you are already in a Medicare Advantage plan, a separate window in the first few months of the following year gives you one more chance to change your mind. And if something happens to your coverage outside either window — a move, a lost job coverage, a plan leaving your area — a Special Enrollment Period may open regardless of the date. AEP is simply the one window that is always there, every year, for anyone who wants to use it.