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Medicare Annual Enrollment Period Guide

Medicare Enrollment Periods: AEP vs. OEP

When navigating the world of Medicare coverage, it's important to understand the key enrollment periods that determine when you can sign up for, switch, or make changes to your coverage. Two critical enrollment windows are the Annual Enrollment Period (AEP) and the Open Enrollment Period (OEP). While they may sound similar, each serves a distinct purpose and has different rules that can impact your health insurance choices.

Medicare Annual Enrollment Period (AEP)

The Medicare Annual Enrollment Period—also known as AEP—allows Medicare beneficiaries to examine their current coverage and make changes if necessary. As Medicare plans can change from year to year, AEP gives beneficiaries the chance to evaluate their coverage and determine if it’s still right for their needs or if they need to make a change.

Key Dates for AEP

The Annual Enrollment Period runs each year from October 15 through December 7.

Changes You Can Make During AEP

During AEP, Medicare beneficiaries can:

Switch from Original Medicare (Medicare Part A and Medicare Part B) to a Medicare Advantage plan (Medicare Part C).
Change from one Medicare Advantage plan to another Medicare Advantage plan.
Switch from one Prescription Drug plan (Medicare Part D) to another or enroll in a Medicare Advantage Prescription Drug plan.
Add a Prescription Drug plan if you didn’t enroll when first eligible for Medicare.

Additional Details

Any changes you make during the Medicare Advantage and Prescription Drug Plan Annual Enrollment Period will take effect on January 1 of the following year. Keep in mind that AEP is a short window, and missing the December 7 deadline generally means that you will have to wait until the next year’s AEP to make changes unless you qualify for a Special Enrollment Period (SEP) due to specific life events, like moving, losing coverage, or becoming newly eligible for Original Medicare.

Medicare Advantage Open Enrollment Period (OEP)

The Medicare Advantage Open Enrollment Period—also known as OEP—allows Medicare Advantage plan beneficiaries to make a one-time plan change. Unlike AEP, OEP is exclusively for individuals enrolled in a Medicare Advantage plan, and only one plan change is allowed during this period. Read on to learn more about OEP.

Key Dates for OEP

The Medicare Advantage Open Enrollment Period runs from January 1 to March 31 each year.

Changes You Can Make During OEP

During OEP, Medicare Advantage beneficiaries can:

Switch to a different Medicare Advantage plan
Drop a Medicare Advantage plan and return to Original Medicare (Medicare Part A and Medicare Part B)
Sign up for a stand-alone Medicare Part D plan, if electing to return to Original Medicare

Additional Details

For those enrolled in a Medicare Advantage plan, only one switch is allowed during OEP. If you sign up for a Medicare Advantage plan during AEP and decide you don’t like the plan once it takes effect in January, you have until March 31 to make a change. You can also only sign up for Part D coverage during the first three months of the year if you’re switching from a Medicare Advantage plan back to Original Medicare (Parts A and B).

Comparing AEP vs. OEP: Key Differences

It’s important to know the differences between AEP and OEP so you’re fully informed about the changes you can make during each enrollment period. The key differences between AEP and OEP include:

Enrollment Period	Dates	Eligibility	Purpose
AEP	October 15-December 7	Open to all Medicare beneficiaries, regardless of whether they are on Original Medicare or a Medicare Advantage plan.	Designed as the main opportunity for all Medicare beneficiaries to review and adjust their coverage for the upcoming year.
OEP	January 1-March 31	Available only to those enrolled in a Medicare Advantage plan. If you’re on Original Medicare, OEP does not apply.	Primarily aimed at helping those with Medicare Advantage plans adjust their coverage if they experience issues with their current plan or wish to make a change after the AEP window has closed.

Understanding When to Enroll in Medicare: OEP vs. AEP

The right time to enroll in a Medicare plan will be similar yet different for everybody. You first become eligible to enroll in Original Medicare three months before your 65th birthday, thus kicking off the Initial Enrollment Period. However, as benefits and costs can change every year, it can be extremely beneficial to revisit your coverage on an annual basis to make sure your plan is still the right fit for you.

All Medicare beneficiaries are eligible to change their coverage during AEP in the fall, but only Medicare Advantage enrollees can make adjustments during OEP at the beginning of the calendar year. Even if you’re satisfied with your Medicare coverage, AEP is a great opportunity to compare all of the options available to you, ensuring you’re getting all the benefits you deserve. If you’ve enrolled in a Medicare Advantage plan and decide it’s no longer the right fit for you, you can reevaluate your options during OEP for a one-time change.

See when the right time for you to enroll might be.

Evaluating Your Current Coverage

When evaluating your current Medicare plan coverage, ask yourself the following questions to ensure your plan still meets your needs:

Are my healthcare providers still covered?
Do my prescription drugs continue to be covered?
Has my health status changed?
Are the premiums, deductibles, and out-of-pocket costs still affordable?
Should I consider switching to a Medicare Advantage or Part D plan?
Are there any upcoming changes to my plan or healthcare needs?

Answering these questions will help you assess whether your current coverage is still the best option for you or if changes are needed during the upcoming enrollment period.

Where to Get Help or Information

For questions about AEP, OEP, or other Medicare-related concerns, you can call Medicare’s official phone number at 1-800-633-4227. TTY users can call 1-877-486-2048.

AEP vs. OEP FAQs

Is AEP the best time to sign up for Medicare for the first time?

If you're new to Medicare, you should enroll during your Initial Enrollment Period (IEP), which starts three months before you turn 65 and ends three months after your 65th birthday. If you miss your IEP, you may have to wait for the next AEP, which could result in delayed coverage and potential late enrollment penalties.

Can I switch Medicare Advantage plans during both periods?

Yes, you can switch Medicare Advantage plans during both AEP (October 15 to December 7) and OEP (January 1 to March 31), but with different conditions. During AEP, anyone with Medicare can switch to a different Medicare Advantage plan or change to Original Medicare with or without a Part D plan. During OEP, you can only switch Medicare Advantage plans if you’re already enrolled in one.

Can I switch from Original Medicare to Medicare Advantage during both periods?

Yes, you can switch from Original Medicare to Medicare Advantage during both AEP and OEP. During AEP (October 15 to December 7), you can make this change for the upcoming year, and during OEP (January 1 to March 31), you can switch from Original Medicare to Medicare Advantage if you're already enrolled in Original Medicare.

Can I change plans more than once during OEP?

No, you can only make one plan change per OEP. Any changes made will take effect the first of the month following your request.

What is an Annual Notice of Change (ANOC)?

An Annual Notice of Change (ANOC) is a document that your Medicare Advantage or Part D plan sends you each year to notify you of any changes to your coverage for the upcoming year. This may include changes to premiums, deductibles, coverage benefits, formularies, and provider networks. It is important to review your ANOC to ensure your current plan still meets your needs for the next year.

Do I have to enroll in Medicare every year?

No, once you’re enrolled in Medicare, you generally don’t need to enroll every year unless you want to make changes to your coverage. However, during AEP or OEP, you can switch plans or update your coverage options. If you're already enrolled in Medicare, your coverage will automatically renew, but you should still review your plan to ensure it fits your needs.

What happens if I miss the deadlines for AEP and OEP?

If you miss the deadlines for AEP (October 15 to December 7) and OEP (January 1 to March 31), you may not be able to make changes to your coverage until the next year unless you qualify for a Special Enrollment Period (SEP). SEPs are granted for specific life events, such as moving or losing coverage. Missing these enrollment periods without a valid SEP could result in a gap in coverage or potential penalties, especially if you delay enrolling in a Medicare plan.

Let SelectQuote help you with your Medicare Advantage plan options.

All of the terminology associated with Medicare enrollment can be confusing, but our licensed insurance agents can save you time by reviewing Medicare Advantage plans that may be available in your area. The service is free, and there’s no obligation to enroll.

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Explore the Medicare Annual Enrollment Period Guide for 2026 Coverage