Medicare’s Annual Enrollment Period: What It Is and How It Really Works

If you’re on Medicare, the Annual Enrollment Period (AEP) is the main window each year when you can change how you get your coverage. Missing it can mean you’re stuck with a plan you don’t like for another year, so it’s worth understanding exactly what this period allows you to do.

When is the Medicare Annual Enrollment Period?

The Annual Enrollment Period runs every year from October 15 through December 7.
Any changes you make during this time take effect January 1 of the following year.

This period is sometimes called Fall Open Enrollment or just Medicare Open Enrollment, but it specifically applies to Medicare Advantage (Part C) and Medicare prescription drug (Part D) plans.

What can you do during Annual Enrollment?

During AEP, you can:

• Join a Medicare Advantage plan if you currently have Original Medicare.
• Switch from one Medicare Advantage plan to another (with or without drug coverage).
• Drop Medicare Advantage and return to Original Medicare (Part A and Part B).
• Join a Part D prescription drug plan if you don’t have one.
• Switch from one Part D plan to another.
• Drop Part D coverage entirely.

You generally cannot use AEP to enroll in a Medigap (Medicare Supplement) policy with guaranteed acceptance; Medigap has its own rules and enrollment protections.

How AEP differs from other Medicare enrollment periods

People often confuse AEP with other timeframes. A quick way to keep them straight:

• Initial Enrollment Period (IEP): Your first chance to sign up for Medicare around your 65th birthday or when you first qualify.
• Special Enrollment Periods (SEPs): Limited-time windows triggered by specific events, such as moving out of your plan’s service area, losing employer coverage, or qualifying for certain types of assistance.
• Medicare Advantage Open Enrollment Period (MA OEP): January 1–March 31 each year, when people already in a Medicare Advantage plan can switch to another Advantage plan or go back to Original Medicare (with a chance to join Part D). This is different from AEP and more limited.

AEP is the main, predictable, once-a-year opportunity for most people to review and change their Medicare Advantage and Part D coverage.

Why the Annual Enrollment Period matters

Medicare Advantage and Part D plans can change their premiums, copays, drug formularies, provider networks, and extra benefits every year. Even if your plan name stays the same, your costs and coverage might not.

Using AEP to compare options can help you:

• Avoid surprise drug costs if your medications move to a higher tier or drop off a formulary.
• Keep access to your preferred doctors and pharmacies if networks change.
• Adjust coverage if your health needs, prescriptions, or budget have shifted.

Each fall, plans send an Annual Notice of Change, outlining what will be different next year. Reviewing that document and using the AEP window to act on it is one of the most important parts of managing your Medicare coverage.

In short, the Medicare Annual Enrollment Period is your yearly chance to reset your Medicare Advantage and Part D coverage so it lines up with your current health needs and financial situation. Treat those weeks between October 15 and December 7 as a recurring appointment to protect your coverage for the year ahead.