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Medicare Enrollment Periods, Explained Clearly

Medicare has four separate enrollment periods, each with its own dates and its own rules for what you're allowed to change. Confusing one for another is one of the most common mistakes I see, and it can mean missing your window entirely. Here's how each one works.

The Four Medicare Enrollment Periods

Initial Enrollment Period (Turning 65)

Your Initial Enrollment Period is the seven-month window built around your 65th birthday, three months before, your birthday month, and three months after. This is your first opportunity to enroll in Medicare Parts A and B, and missing it can mean a lasting late enrollment penalty. If you're approaching 65, this is the period that applies to you.


Turning 65 in New Jersey →

Annual Enrollment Period (AEP)

AEP runs every year from October 15 through December 7. During this window, anyone with Medicare can switch between Original Medicare and Medicare Advantage, join or switch a Medicare Advantage plan, or join, drop, or switch a Part D prescription drug plan. Changes made during AEP take effect January 1 of the following year. This is the broadest and most well-known enrollment period, and the one most of the mail you receive each fall is about.

Medicare Advantage Open Enrollment Period

This period runs every year from January 1 through March 31, and it's more limited than AEP. It's only available if you're already enrolled in a Medicare Advantage plan, and it allows one change: switching to a different Medicare Advantage plan, or switching back to Original Medicare. You can't use this period to join a new Part D plan unless you're also returning to Original Medicare. This is the period most often confused with AEP, since both fall in the same general Medicare season but allow different changes.

Special Enrollment Periods

Special Enrollment Periods aren't tied to a calendar window. Instead, they're triggered by specific life events, such as moving out of your plan's service area, losing employer or other coverage, or your plan being discontinued. The length of the window and what you're allowed to change depends on the specific event, so it's worth confirming your situation rather than assuming a general rule applies.

AEP vs. Medicare Advantage Open Enrollment: What's the Difference?

These two periods are the ones most commonly confused, since both happen in a similar timeframe each year. AEP is open to everyone with Medicare and allows the widest range of changes. The Medicare Advantage Open Enrollment Period only applies if you're already enrolled in a Medicare Advantage plan, and it allows just one plan switch.


  • AEP: Available to all Medicare beneficiaries; October 15–December 7
  • MA Open Enrollment Period: Available only to current Medicare Advantage enrollees; January 1–March 31
  • AEP allows joining, dropping, or switching Advantage and Part D plans
  • MA Open Enrollment Period allows one switch, either to a different Advantage plan or back to Original Medicare
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Frequently Asked Questions

  • When is the Medicare Annual Enrollment Period in 2026?

    AEP runs from October 15 through December 7 every year. Any changes made during this window take effect on January 1 of the following year.

  • What's the difference between AEP and open enrollment?

    AEP and the Medicare Advantage Open Enrollment Period are sometimes both called "open enrollment," which causes confusion. AEP runs in the fall and is open to everyone with Medicare, while the Medicare Advantage Open Enrollment Period runs January through March and only applies if you're already enrolled in a Medicare Advantage plan.

  • Can I change my Medicare plan outside of AEP?

    Yes, in specific situations. If you're already in a Medicare Advantage plan, you can make one change during the Medicare Advantage Open Enrollment Period from January through March. Outside of both windows, a Special Enrollment Period triggered by a qualifying life event may also allow changes.

Explore Your Coverage Options

Medicare Advantage

All-in-one coverage combining hospital, medical, and often prescription drug benefits.

Medicare Supplements

Coverage that pairs with Original Medicare to reduce your out-of-pocket costs.

Serving Ocean County Seniors, Face-to-Face

If you're in Ocean County or the surrounding area, I meet with clients in person to sort out exactly which enrollment period applies to their situation.

Not Sure Which Period Applies to You?

Every Medicare enrollment period has different rules for what you're allowed to change, and getting it wrong can mean waiting a full year to fix it. Call or text, and I'll help you figure out exactly which window matters for your situation.