When to Enroll in Medicare: Key Enrollment Periods

Initial Enrollment Period (IEP)

Your Initial Enrollment Period is a 7-month window surrounding your 65th birthday. It begins 3 months before the month you turn 65, includes your birthday month, and extends 3 months after your birthday month.

During this period, you can sign up for Medicare Part A, Part B, a Medicare Advantage plan, and a Part D prescription drug plan. If you are already receiving Social Security benefits, you will typically be enrolled in Parts A and B automatically.

Enrolling during your IEP is important because it ensures coverage starts promptly and avoids late enrollment penalties. If you sign up during the 3 months before your birthday month, coverage typically starts the first day of your birthday month.

Annual Enrollment Period (AEP)

The Annual Enrollment Period runs from October 15 through December 7 each year. During this window, you can make changes to your Medicare coverage that take effect on January 1 of the following year.

During the AEP, you can switch from Original Medicare to a Medicare Advantage plan, switch from a Medicare Advantage plan back to Original Medicare, change from one Medicare Advantage plan to another, join a Part D prescription drug plan, switch Part D plans, or drop Part D coverage.

This is the primary enrollment period for comparing and changing plans. Insurance companies release their plan details for the coming year on October 1, giving you two weeks to review options before the enrollment window opens.

Medicare Advantage Open Enrollment Period (MA OEP)

The Medicare Advantage Open Enrollment Period runs from January 1 through March 31 each year. This period is specifically for people who are already enrolled in a Medicare Advantage plan.

During the MA OEP, you can switch from one Medicare Advantage plan to another, drop your Medicare Advantage plan and return to Original Medicare (and join a stand-alone Part D plan), but you cannot use this period to go from Original Medicare to a Medicare Advantage plan.

Changes made during the MA OEP take effect the first of the month after the plan receives your request.

Special Enrollment Periods (SEPs)

Special Enrollment Periods allow you to make changes to your Medicare coverage outside of the standard enrollment windows when certain qualifying life events occur.

Common qualifying events include losing employer or union health coverage, moving out of your plan's service area, qualifying for Medicaid or Extra Help (Low Income Subsidy), entering or leaving a nursing home, experiencing a plan contract violation by your insurer, or being affected by a natural disaster.

If you are still working and have employer coverage when you turn 65, you have a Special Enrollment Period that begins when your employment or employer coverage ends (whichever comes first) and lasts for 8 months.

Late Enrollment Penalties

If you do not enroll in Medicare when you are first eligible and do not qualify for a Special Enrollment Period, you may face permanent late enrollment penalties.

The Part B late enrollment penalty adds 10% to your Part B premium for each full 12-month period you were eligible but did not enroll. This penalty applies for as long as you have Part B.

The Part D late enrollment penalty is calculated by multiplying 1% of the national base beneficiary premium by the number of months you went without creditable drug coverage. This penalty is also added to your Part D premium permanently.

These penalties are applied to your premium for the rest of your life, making timely enrollment critically important.