Quick Reference

Enrollment Period When What You Can Do
Initial Enrollment Period (IEP) 7 months around your 65th birthday First enrollment in Parts A, B, C, D
Annual Enrollment Period (AEP) October 15 – December 7, every year Join/switch/drop MA and Part D plans for Jan 1
MA Open Enrollment (MA-OEP) January 1 – March 31 One switch if you're already on Medicare Advantage
General Enrollment Period (GEP) January 1 – March 31 Sign up for Part B if you missed your IEP
Special Enrollment Periods (SEPs) Triggered by life events Varies by qualifying event
Medigap Open Enrollment 6 months from Part B enrollment at 65+ Buy any Medigap plan, no health questions

Initial Enrollment Period: Your First Window

Your IEP lasts seven months: the three months before your 65th birthday month, your birthday month, and the three months after. This is when you first enroll in Medicare Part A and Part B, and when you can choose a Medicare Advantage plan or a Part D drug plan. Enrolling in the three months before your birthday month means coverage starts the first day of your birthday month - the smoothest possible transition. Our full Turning 65 checklist walks through this step by step, including what to do if you're still working at 65.

Annual Enrollment Period: October 15 – December 7

AEP is the big one - the window that applies to everyone on Medicare, every year. Between October 15 and December 7, you can:

  • Switch from Original Medicare to a Medicare Advantage plan, or back
  • Switch from one Medicare Advantage plan to another
  • Join, drop, or switch a standalone Part D drug plan

Everything you do during AEP takes effect January 1 of the coming year.

Why does AEP matter even if you like your current plan? Because your plan changes even when you don't. Every September, plans mail an Annual Notice of Change (ANOC) describing next year's premiums, copays, formulary changes, provider network changes, and benefit changes. Carriers also enter and exit counties each year, meaning stronger options may exist next year that didn't exist when you enrolled. Reviewing your ANOC and comparing the new plan landscape each fall is the single highest-value hour in Medicare - and it's an hour our licensed agents will do with you at no cost. Call 888-918-6920 before December 7.

Medicare Advantage Open Enrollment: January 1 – March 31

If you're already enrolled in a Medicare Advantage plan on January 1, the MA-OEP gives you one mid-course correction: a single switch to a different Medicare Advantage plan, or a return to Original Medicare (with the option to add a Part D plan). You cannot use MA-OEP to move from Original Medicare into Medicare Advantage, and you can't use it to switch standalone Part D plans. It exists as a safety valve - if your January claims reveal your new plan isn't what you expected, you have until March 31 to fix it.

General Enrollment Period: January 1 – March 31

If you missed your IEP and don't qualify for a Special Enrollment Period, the GEP is when you can sign up for Part B (and premium Part A). Coverage starts the month after you enroll. Late enrollment penalties may apply - the Part B penalty adds 10% to your premium for each full 12-month period you could have had Part B but didn't, and it lasts as long as you have Part B. This is the outcome good planning avoids.

Special Enrollment Periods: When Life Doesn't Follow the Calendar

SEPs let you make changes outside the standard windows when specific events occur. Common qualifying events include:

  • Leaving employer coverage. Working past 65 with qualifying employer group coverage? You get an 8-month SEP for Part B starting when employment or coverage ends (and a 2-month window for Part D/MA) - no penalty.
  • Moving out of your plan's service area, or moving somewhere with new plan options.
  • Losing other coverage (Medicaid, employer, retiree, or creditable drug coverage).
  • Gaining or losing Medicaid or Extra Help eligibility. People with both Medicare and Medicaid, or with Extra Help, have ongoing opportunities to change plans - see Dual-Eligible Special Needs Plans.
  • Your plan leaves Medicare or leaves your area.
  • Qualifying for a Special Needs Plan - for example, a diagnosis that qualifies you for a Chronic Condition SNP allows enrollment when the diagnosis occurs, not just in the fall.
  • 5-star plans. If a plan rated 5 stars by Medicare is available in your area, you can switch into it once per year (December 8 – November 30)

SEP rules are precise about timing and documentation. If a life change is coming - retirement, a move, a change in Medicaid status - talk to an agent before it happens so nothing lapses.

Medigap's Timing Is Different - and Less Forgiving

Medigap doesn't follow AEP. Your one guaranteed window is the six-month Medigap Open Enrollment Period starting the month you're 65+ and enrolled in Part B: during it, carriers must accept you regardless of health. Afterward, in most states, applications can be medically underwritten. If a Medicare Supplement is part of your plan, timing it correctly matters more than for any other product. Full details: Medicare Supplement plans.

Mark Your Calendar

  • September: Read your ANOC the week it arrives.
  • October 1: Next year's plan details become public; agents can discuss them.
  • October 15 - December 7: AEP - compare and enroll.
  • January 1: New coverage takes effect.
  • January 1 - March 31: MA-OEP safety valve.

One call with a licensed MegaCare agent confirms exactly which windows apply to you and what your options are inside them.

Call 888-918-6920 TTY: 711, Mon-Fri 9am-6pm EST

Frequently Asked Questions

  • When is Medicare open enrollment?

    The Annual Enrollment Period runs October 15 through December 7 every year, with changes effective January 1.

  • Can I change my Medicare Advantage plan after December 7?

    If you're enrolled in a Medicare Advantage plan, you get one switch between January 1 and March 31 (MA-OEP). Otherwise you'll need a qualifying Special Enrollment Period.

  • I'm still working at 65. Do I have to enroll?

    If you have qualifying employer group coverage (generally from an employer with 20+ employees), you can typically delay Part B without penalty and use a Special Enrollment Period when you retire. Confirm your situation before your 65th birthday - the rules differ for smaller employers and COBRA.

  • What happens if I do nothing during AEP?

    Your current plan renews with whatever changes its ANOC described - new copays, formulary, and network included. Doing nothing is still a decision; make it an informed one.

  • Is there a penalty for late Part D enrollment?

    Yes - a permanent premium penalty accrues for each month you go without creditable drug coverage beyond 63 days after your IEP. See Medicare Part D.