Medicare enrollment periods: IEP, AEP, and OEP explained
Medicare has set windows when you can sign up or change your coverage. The three most common are the Initial Enrollment Period (IEP) when you first become eligible, the Annual Enrollment Period (AEP) each fall, and the Medicare Advantage Open Enrollment Period (OEP) in the first part of the year.
Initial Enrollment Period (IEP)
Your IEP is the seven-month window around your 65th birthday: the three months before the month you turn 65, the month itself, and the three months after. This is when most people first sign up for Parts A and B and choose how to get drug coverage. Signing up on time helps you avoid late-enrollment penalties.
Annual Enrollment Period (AEP)
AEP runs from October 15 to December 7 every year. During AEP anyone with Medicare can join, switch, or drop a Medicare Advantage or Part D plan, with changes taking effect January 1. This is the main window for reviewing your coverage as plans change their costs and formularies each year.
Open Enrollment Period (OEP)
The Medicare Advantage Open Enrollment Period runs from January 1 to March 31. If you are already in a Medicare Advantage plan, you can switch to a different Advantage plan or return to Original Medicare (and add a Part D plan) once during this window. Other special enrollment periods exist for life events. For your exact dates and options, contact Medicare.gov, 1-800-MEDICARE, or your SHIP.
Frequently asked questions
When can I first sign up for Medicare?
Most people use their Initial Enrollment Period — the seven months around their 65th birthday (three months before, the birthday month, and three months after).
What's the difference between AEP and OEP?
AEP (Oct 15–Dec 7) is when anyone can join, switch, or drop Advantage and Part D plans. OEP (Jan 1–Mar 31) is a more limited window for people already in a Medicare Advantage plan to make one change.
This is general education, not personalized advice, and plan details change every year. For all of your options, contact Medicare.gov, 1-800-MEDICARE, or your local State Health Insurance Assistance Program (SHIP) at shiphelp.org.