When to Sign Up for Medicare: Enrollment Periods Explained (IEP, AEP, OEP & SEP)

Timing is one of the most important parts of Medicare, because signing up late can mean paying a penalty for as long as you have coverage. Here is a plain-English guide to when to sign up for Medicare -- every enrollment window and how to avoid late-enrollment penalties.

Initial Enrollment Period (IEP): the 7-month window

Your first chance to sign up is the Initial Enrollment Period -- a 7-month window that includes the 3 months before your 65th birthday month, your birthday month, and the 3 months after. Signing up in the first 3 months helps your coverage start as early as possible. This is the on-time window that keeps you clear of late penalties.

Annual Enrollment Period (AEP): October 15 - December 7

Each fall, anyone with Medicare can join, switch, or drop a Medicare Advantage or Part D plan. Changes made during AEP take effect January 1. This is the main window to review your plan against next year's benefits and drug costs.

Medicare Advantage Open Enrollment: January 1 - March 31

If you are already in a Medicare Advantage plan on January 1, you get one chance during this window to switch to a different Medicare Advantage plan or go back to Original Medicare (and add a Part D plan). It does not apply to people who only have Original Medicare.

General Enrollment Period: January 1 - March 31

If you missed your Initial Enrollment Period and do not qualify for a Special Enrollment Period, you can sign up for Part A and/or Part B during this window, with coverage starting the month after you enroll. A late-enrollment penalty may apply.

Special Enrollment Periods (SEP)

Life events can open a Special Enrollment Period outside the normal windows -- losing employer coverage, moving out of your plan's service area, a plan leaving Medicare, and others. If you are working past 65 with qualifying employer coverage, an SEP often lets you delay Part B and enroll later without penalty. See our turning 65 guide for how this fits the bigger picture.

Avoiding late-enrollment penalties

The Part B and Part D late-enrollment penalties can last a lifetime. The simplest way to avoid them is to enroll during your Initial Enrollment Period, or to keep creditable coverage and use a Special Enrollment Period when it ends.

Frequently asked questions

When is my Initial Enrollment Period?

Your Initial Enrollment Period (IEP) is a 7-month window around your 65th birthday: the 3 months before your birthday month, your birthday month, and the 3 months after. This is when most people first sign up for Medicare.

What is the difference between AEP and Open Enrollment?

The Annual Enrollment Period (AEP), October 15 to December 7, is when anyone with Medicare can join, switch, or drop a Medicare Advantage or Part D plan for the next year. The Medicare Advantage Open Enrollment Period, January 1 to March 31, lets people already in a Medicare Advantage plan make a one-time switch or return to Original Medicare.

What happens if I sign up late?

If you do not sign up for Part B when first eligible and do not have other qualifying coverage, you may pay a Part B late-enrollment penalty for as long as you have Medicare. Going without creditable drug coverage can create a lifelong Part D penalty as well. Signing up during your Initial Enrollment Period avoids both.

Can I delay Medicare if I am still working?

Often yes. If you have qualifying employer coverage through your own or a spouse's active employment, you may be able to delay Part B without penalty and use a Special Enrollment Period to sign up later. Confirm your specific situation before declining Part B.

What is a Special Enrollment Period?

A Special Enrollment Period (SEP) lets you make changes outside the normal windows after certain life events -- for example losing employer coverage, moving out of your plan's service area, or a plan leaving your area. The rules and timing depend on the event.