Medicare Enrollment Periods Explained
Knowing when you can enroll, switch, or make changes - and what happens if you miss your window - is one of the most important parts of Medicare planning.
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The Four Main Medicare Enrollment Periods
Medicare has specific windows when you can enroll or make changes. Outside these windows, your options are limited.
Your first opportunity to enroll in Medicare. The IEP runs for 7 months - starting 3 months before your birthday month, including your birthday month, and ending 3 months after. This is when you first become eligible for Parts A, B, and D, and can choose a Medicare Advantage or Medigap plan.
- •Enroll in the first 3 months for earliest coverage start
- •Enrolling during or after your birthday month may delay coverage
- •Missing IEP without qualifying coverage may result in late penalties
- •Use this window to set up your full Medicare coverage path
The AEP (sometimes called the Fall Open Enrollment Period) runs from October 15 to December 7 each year. During this time, people already enrolled in Medicare can review and make changes to their coverage for the following year. Changes made during AEP take effect January 1.
- •Switch between Medicare Advantage and Original Medicare
- •Add, drop, or change a Part D prescription drug plan
- •Switch from one Medicare Advantage plan to another
- •Review your plan's Annual Notice of Change (ANOC) before deciding
If you are already enrolled in a Medicare Advantage plan, you can use the MA-OEP to make a one-time change. This period runs from January 1 through March 31. Changes take effect the first of the month after the plan receives your enrollment request.
- •Available only to those already enrolled in a Medicare Advantage plan
- •One change allowed during this period
- •Can switch to another Medicare Advantage plan
- •Can switch to Original Medicare (and add a Part D plan)
- •Cannot use this period to switch from Original Medicare to MA
An SEP is a time-limited enrollment window that opens when you experience a qualifying event. SEPs allow changes outside the standard enrollment windows. Each SEP has its own rules about what changes you can make and for how long the window remains open.
- •Moving to a new service area (ZIP code or county change)
- •Losing qualifying employer or union coverage
- •Gaining or losing Medicaid or Extra Help
- •Returning from overseas or a correctional facility
- •Plan termination or material reduction in coverage
Quick Reference: Enrollment Period Calendar
| Period | When | Who It’s For | What You Can Do |
|---|---|---|---|
| IEP | 7 months around your 65th birthday | First-time Medicare enrollees | Enroll in Parts A, B, D, MA, or Medigap |
| AEP | Oct 15 – Dec 7 | All Medicare beneficiaries | Switch plans, add/drop Part D, change MA plans |
| MA-OEP | Jan 1 – Mar 31 | Current MA plan members only | One plan change - MA to MA or MA to Original Medicare |
| SEP | Based on qualifying event | Those with a qualifying life event | Varies by event type - enroll or switch |
Penalties for Missing Your Enrollment Window
If you miss your Initial Enrollment Period without qualifying coverage in place, you may face late enrollment penalties and delays in coverage. These penalties are generally permanent - added to your premium for as long as you have that coverage.
Part B Late Penalty
For each 12-month period you were eligible for Part B but did not enroll (without qualifying employer coverage), your Part B premium may increase by 10%. This penalty is added to your premium for as long as you have Part B - it does not expire.
Part D Late Penalty
If you go without creditable prescription drug coverage for 63 or more consecutive days after your IEP, you may owe a monthly late enrollment penalty added to your Part D premium. Whether the penalty applies depends on your coverage history.
Important: Employer or union coverage, VA benefits, TRICARE, and certain other coverage may allow you to delay enrollment without penalty - but eligibility rules vary. Always verify your situation before delaying Medicare enrollment.
Not Sure Which Enrollment Window Applies to You?
A licensed agent can review your specific situation - whether you’re approaching 65, on Medicare through disability, or dealing with a qualifying life event.