Medicare reference · 6 min read
Medicare Enrollment Periods: IEP, GEP, AEP, and SEPs
Medicare has four main enrollment windows. Your Initial Enrollment Period (IEP) is the 7 months around your 65th birthday. The General Enrollment Period (Jan 1–Mar 31) is for people who missed their IEP. The Annual Enrollment Period, or Open Enrollment (Oct 15–Dec 7), is when anyone with Medicare can change drug or Advantage plans for the next year. Special Enrollment Periods (SEPs) are triggered by life events like losing employer coverage.
Initial Enrollment Period (IEP)
Your IEP is the first time you can sign up — a 7-month window that begins 3 months before the month you turn 65, includes your birthday month, and ends 3 months after. Signing up early (before your birthday month) avoids a gap in coverage.
General Enrollment Period (GEP)
If you missed your IEP and do not qualify for a Special Enrollment Period, you can sign up for Part A and/or Part B during the General Enrollment Period, January 1 through March 31 each year. Coverage starts the first day of the month after you enroll. A late-enrollment penalty may apply.
Annual Enrollment Period (AEP / Open Enrollment)
From October 15 to December 7 each year, anyone with Medicare can join, switch, or drop a Medicare Advantage plan or a Part D drug plan. Changes take effect January 1. This is the main window to review your coverage for the coming year.
Medicare Advantage Open Enrollment
From January 1 to March 31, if you are already in a Medicare Advantage plan you can switch to a different Advantage plan or drop back to Original Medicare (and join a Part D plan). You can only use this window once per year.
Special Enrollment Periods (SEPs)
Certain life events open a Special Enrollment Period — for example, losing employer coverage, moving out of your plan’s service area, or qualifying for Extra Help. SEPs let you enroll or change plans outside the normal windows, usually without a penalty.
Common questions
Can I change my Medicare Advantage plan any time?
No. You can change during the Annual Enrollment Period (Oct 15–Dec 7), the Medicare Advantage Open Enrollment Period (Jan 1–Mar 31), or if you qualify for a Special Enrollment Period.
What is the difference between the GEP and AEP?
The General Enrollment Period (Jan 1–Mar 31) is for first-time sign-up if you missed your IEP. The Annual Enrollment Period (Oct 15–Dec 7) is for changing drug or Advantage plans you already have.
Sources
CreditMango is independent and not affiliated with or endorsed by Medicare, CMS, the Social Security Administration or any insurer. This is general information for 2026, not medical, insurance or financial advice; rules and costs change every year. For free, unbiased one-on-one help, contact your State Health Insurance Assistance Program (SHIP) at shiphelp.org ↗ or call 1-800-MEDICARE.