Medicare Enrollment Periods, Mapped to the Calendar
Five windows, five purposes. Here's exactly when each one opens and closes.
Last reviewed: August 2026 · Reviewed for accuracy by a licensed Medicare agent (Paul)
Fixed enrollment windows across the year
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
General Enrollment (Jan 1–Mar 31)
MA Open Enrollment (Jan 1–Mar 31)
Annual Enrollment (Oct 15–Dec 7)
Initial Enrollment Period
Not shown above — it's a personal 7-month window built around your own 65th birthday, not a fixed calendar date. See the
turning 65 timeline.
Special Enrollment Period
Also not fixed — it opens whenever a qualifying life event happens, such as losing employer coverage.
Medicare has five main enrollment periods, each with a different purpose and window. Missing the right one can mean waiting months to enroll or make changes — sometimes with a penalty attached.
The five periods, one at a time
Initial Enrollment Period (IEP)
7 months around your 65th birthday
Your first chance to enroll, spanning 3 months before, the month of, and 3 months after your 65th birthday. See our
turning 65 timeline for a month-by-month breakdown.
General Enrollment Period (GEP)
January 1 – March 31
If you didn't sign up during your IEP and don't have a qualifying reason to delay, you'll need to wait for this window. Coverage typically starts the month after you enroll, and a late-enrollment penalty may apply.
Special Enrollment Period (SEP)
Varies — triggered by a life event
Triggered by specific events, most commonly losing employer or union group coverage. The length and rules of a SEP depend on the triggering event, so it's worth confirming your exact window rather than assuming a standard timeframe.
Annual Enrollment Period (AEP)
October 15 – December 7
The main "open season" for Medicare. Every year, you can switch Medicare Advantage plans, switch between Original Medicare and Medicare Advantage, or change your Part D drug plan. Changes take effect January 1.
Medicare Advantage Open Enrollment (MA OEP)
January 1 – March 31
A shorter window early in the year for people already in a Medicare Advantage plan to make one switch — either to a different Advantage plan or back to Original Medicare with a Part D plan.
Not sure which enrollment period applies to you?
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Frequently asked questions
Can I use more than one enrollment period in the same year?
Generally you can only make one plan change per period, and periods serve different purposes, so which one applies depends on your specific situation and timing.
What's the difference between AEP and MA OEP?
AEP (fall) allows broader changes across Original Medicare, Medicare Advantage, and Part D. MA OEP (early in the year) is limited to those already enrolled in a Medicare Advantage plan making one switch.
Do Special Enrollment Periods have penalties?
Typically no, if you qualify for a genuine SEP and enroll within its window, since the SEP exists to avoid penalizing you for a change outside your control.