Medicare Enrollment Periods Explained: What You Need to Know for 2025
Find out how and when you can enroll in Medicare, switch plans, and avoid late penalties. Get the details on IEP, OEP, AEP, and Medigap, plus what matters for Medicare Advantage and drug plans.
Understanding Medicare Enrollment Periods
Medicare has set times during the year when you can enroll, make changes, or add coverage. Missing a window can cause penalties or delays. The tool below shows your basic personal windows.
Check Your Windows
Enter your date of birth. See your Initial Enrollment Period and your Medigap Open Enrollment window.
This is a quick guide. Special situations (like delayed Part B because of work coverage) can change timing.
Medicare Enrollment Periods
Enter your birthdate to see when you can enroll in Medicare and Medigap.
Below we break down each national enrollment period in plain terms so you know what action fits where.
1. Initial Enrollment Period (IEP)
The Initial Enrollment Period is your first chance to sign up for Medicare. It’s a 7-month window that starts three months before the month you turn 65, includes your birthday month, and ends three months after. During this time, you can:
- Enroll in Medicare Part A (hospital) and/or Part B (medical)
- Join a Medicare Advantage plan (MAPD)
- Sign up for a Part D prescription drug plan (PDP)
Missing your IEP can mean late enrollment penalties or gaps in coverage. Read our guide on avoiding penalties for more information.
2. Annual Enrollment Period (AEP)
The Annual Enrollment Period runs every year from October 15 to December 7. This is the main time to make changes if you’re already on Medicare. During AEP, you can:
- Switch from Original Medicare to Medicare Advantage
- Go back to Original Medicare
- Join, drop, or switch a Part D drug plan
- Change from one Medicare Advantage plan to another
Your changes take effect January 1 of the next year.
3. Medicare Advantage Open Enrollment Period (OEP)
OEP is from January 1 to March 31. This is only for people already enrolled in a Medicare Advantage plan. During OEP, you can:
- Switch to another Medicare Advantage plan
- Drop your Medicare Advantage plan and return to Original Medicare (with the option to join a Part D drug plan)
You can only make one change during OEP. This period doesn’t apply if you only have Original Medicare.
Medigap Enrollment: Anytime, but Underwriting Matters
Medigap (Medicare Supplement) plans can help pay costs that Original Medicare doesn’t cover. Unlike MAPD or PDP plans, you can apply for a Medigap plan any time of year. But after your initial Medigap Open Enrollment (a 6-month window after you first get Part B), insurance companies can use medical underwriting. This means you could be denied coverage or pay higher premiums based on your health history.
Key tip: To get a Medigap plan without health questions, sign up during your Medigap Open Enrollment window.
Comparison Table: Enrollment Periods
| Enrollment Period | Who Can Use It | What You Can Do | When It Happens |
|---|---|---|---|
| IEP | New to Medicare | Enroll in Part A, B, MAPD, PDP | 7 months around 65th birthday |
| AEP | Anyone on Medicare | Switch/drop MAPD or PDP plans | Oct 15 – Dec 7 each year |
| OEP | MAPD members | Switch/drop MAPD, go to Original Medicare | Jan 1 – Mar 31 each year |
| Medigap OEP | New to Part B | Enroll in Medigap, no health questions | 6 months after Part B starts |
Frequently Asked Questions
What happens if I miss my Initial Enrollment Period?
You could face late enrollment penalties for Part B or Part D, and you may have to wait until the next General Enrollment Period to sign up.
Can I get a Medigap plan any time?
Yes, but after your first 6 months on Part B, you might have to answer health questions and could be turned down or charged more.
How often can I change my Medicare Advantage plan?
You can make changes once a year during AEP or once during OEP if you’re already in a MAPD plan.
When can I join, drop, or switch a Part D drug plan?
You can do this during IEP, AEP, or if you qualify for a Special Enrollment Period.
Can I change from Medicare Advantage back to Original Medicare?
Yes, during AEP or OEP, or if you qualify for a Special Enrollment Period.
What is a Special Enrollment Period?
This is a window for certain life events, like moving, losing other coverage, or qualifying for Medicaid.
The Bottom Line
Medicare enrollment windows can be confusing, but getting familiar with the key dates can save you money and stress. If you need help sorting out your options or have questions about the right plan for you, our team can guide you—just reach out for a free consultation. For more basic information, check out our Medicare Beginner's Guide.