3.2 Annual Enrollment Period (AEP): October 15 – December 7

Why AEP Matters on the Exam

If the IEP is the window every new beneficiary passes through once, the Annual Enrollment Period (AEP) is the window every existing beneficiary passes through every single year. It is the busiest selling season in the Medicare industry, which is exactly why AHIP devotes so much of Module 4 (Marketing & Sales Compliance) to rules that specifically govern AEP conduct — Scope of Appointment, unsolicited contact restrictions, and enrollment procedures all exist largely because of the volume and pressure of this seven-week window.

What AEP Is

AEP runs from October 15 through December 7 every year. Any change a beneficiary makes during AEP takes effect January 1 of the next calendar year, regardless of which day within the window they made it.

What Changes Are Allowed During AEP

AEP is the most permissive enrollment window on the calendar. A beneficiary can move in any direction:

• Original Medicare → Medicare Advantage
• Medicare Advantage → Original Medicare (with or without adding a stand-alone Part D plan)
• Medicare Advantage → a different Medicare Advantage plan
• Stand-alone Part D plan → a different stand-alone Part D plan
• Adding Part D for the first time, or dropping it (subject to the late-enrollment penalty rules in Section 3.5 if dropped without other creditable coverage)

Contrast this with the Medicare Advantage Open Enrollment Period (MA OEP) covered in the next section, which only runs for MA enrollees and only allows one change in one direction — Original Medicare enrollees get no equivalent spring window to switch into MA.

The "Last Choice Wins" Rule

A defining feature of AEP is that beneficiaries may change their selection as many times as they want during the window. CMS only processes the plan selection that is on file as of December 7. If a beneficiary enrolls in Plan A on October 20, switches to Plan B on November 15, and switches again to Plan C on December 5, only Plan C takes effect on January 1 — the two earlier elections are overwritten, not stacked or averaged.

Worked example: Mr. Alvarez enrolls in an HMO plan on October 18 during AEP. On November 30, he calls his agent and asks to switch to a PPO instead. Because it is still before December 7, the switch is valid, and only the PPO enrollment will take effect January 1 — the HMO enrollment is simply superseded, not "kept as a backup."

AEP vs. Other October–December Activity

AEP should not be confused with two other things that happen on a similar calendar:

• Annual Notice of Change (ANOC): Plans mail this document to current members by September 30, before AEP even opens, describing benefit, formulary, and premium changes for the upcoming year. It is not an enrollment window itself — it is the disclosure that informs the AEP decision.
• Medicare & You Handbook: CMS mails this annually, also ahead of AEP, as a general reference — again, not an enrollment mechanism.

Correcting a Mistake Made During AEP

Because AEP allows unlimited changes, correcting an error is simple as long as it is caught before December 7: the beneficiary (or their agent) simply submits a new enrollment request, and the newer request supersedes the old one under the "last choice wins" rule. If the mistake is discovered after December 7 but before the January 1 effective date, CMS treats a timely request to reverse the enrollment as a "void" of the pending election — this is different from disenrolling from an active plan, since the plan hasn't started yet. Once January 1 arrives and the new plan year is underway, undoing an AEP election generally requires either the MA OEP (Section 3.3, if the beneficiary is now MA-enrolled) or a qualifying SEP (Section 3.4) — AEP itself is closed until the following October.

Passive/Default Enrollment Situations

Not every January 1 change traces back to a beneficiary actively picking a new plan during AEP. When a plan is discontinued or leaves the service area, CMS or the parent organization may map affected members into a comparable plan through a "crosswalk" or default/seamless enrollment, effective January 1, unless the beneficiary affirmatively chooses something else during AEP or uses the resulting SEP for plan non-renewal. Agents should always confirm during AEP conversations whether a client's current plan is actually continuing next year — assuming "no news is good news" is a common and costly mistake for beneficiaries who don't realize their plan is being discontinued.

Common Exam Traps

• Thinking AEP changes take effect immediately or on a rolling basis — they always take effect January 1, no matter when during the window the change was made.
• Believing AEP allows unlimited changes throughout the year — the unlimited-changes feature applies only within the October 15–December 7 window itself.
• Confusing AEP with MA OEP: AEP is open to everyone and allows changes in every direction; MA OEP (Section 3.3) is open only to current MA enrollees and allows exactly one change.
• Assuming a beneficiary who does nothing during AEP loses coverage — inaction simply means the beneficiary's current plan continues into the new year (unless the plan itself is being discontinued, which triggers a separate SEP).