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Medicare Enrollment Periods Explained

Initial Enrollment, Annual Enrollment, Special Enrollment, and Medicare Advantage Open Enrollment — know which window applies to you and when it closes.

7 min readReviewed for the 2026 plan year

Medicare · Jenkins Insurance & Retirement

Medicare Enrollment Periods Explained

Initial Enrollment, Annual Enrollment, Special Enrollment, and Medicare Advantage Open Enrollment — know which window applies to you and when it closes.

The Four Main Enrollment Periods

  • Initial Enrollment Period (IEP): 7-month window centered on your 65th birthday month (3 months before, your birthday month, 3 months after).
  • Annual Enrollment Period (AEP): October 15 – December 7 each year. Switch Medicare Advantage or Part D plans for the following year.
  • Medicare Advantage Open Enrollment Period (MA OEP): January 1 – March 31. One plan switch allowed if you're already in a Medicare Advantage plan.
  • Special Enrollment Period (SEP): Triggered by life events like moving, losing employer coverage, or qualifying for Medicaid.

What Happens If You Miss Your Window

Missing your Initial Enrollment Period for Part B can mean a late-enrollment penalty added permanently to your premium, plus a wait until the next General Enrollment Period (January–March, coverage starting the following month).

Key Takeaways

  • Your Initial Enrollment Period is a 7-month window around your 65th birthday — missing it can mean lifetime penalties.
  • AEP (Oct 15–Dec 7) is the main annual window to switch Advantage or Part D plans.
  • Special Enrollment Periods exist for qualifying life events outside the standard windows.

Enrollment rules are set by CMS and can change. Confirm your personal deadlines with a licensed advisor or Medicare.gov.

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