Medicare Annual Enrollment Period vs. Open Enrollment Period Explained

Medicare enrollment periods can be confusing—especially when terms like Annual Enrollment Period (AEP) and Open Enrollment Period (OEP) sound so similar but serve different purposes. AEP runs from October 15 to December 7 each year and is when you can enroll in, switch, or drop Medicare Advantage or Part D plans, while the OEP takes place from January 1 to March 31 and allows those already enrolled in a Medicare Advantage plan to make a one-time change or return to Original Medicare.

Annual Enrollment Period (AEP) Eligibility Requirements

AEP is open to all Medicare beneficiaries, regardless of whether they are on Original Medicare or a Medicare Advantage plan. 

Allowable Actions During AEP

The Annual Enrollment Period (AEP), which runs from October 15 to December 7, is open to anyone enrolled in a Medicare plan, providing the opportunity to review and update coverage for the upcoming year. During AEP, you can take several actions, including:

• Switch from Original Medicare to a Medicare Advantage plan

• Change from one Medicare Advantage plan to another

• Enroll in, switch, or drop a Part D prescription drug plan

• Make changes to your Medigap coverage, if applicable in your state

To make the most of AEP, start by reviewing your Annual Notice of Change letter, which highlights changes to your current plan’s premiums, benefits, or provider network for the next year. Use this information to:

• Compare prescription drug costs under your plan and others

• Check that your preferred doctors and hospitals are still in-network

• Evaluate overall coverage options to ensure they match your healthcare needs

For additional guidance, learn about common Medicare mistakes to avoid, which can help you make informed decisions and prevent costly errors.

Medicare Advantage Open Enrollment Period (OEP) Eligibility Requirements

The Medicare Advantage Open Enrollment Period (OEP) runs January 1 to March 31 each year. This period is only available to individuals already enrolled in a Medicare Advantage (Part C) plan. During OEP, you have one opportunity to make changes to your coverage, including:

• Switching to a different Medicare Advantage plan that may better meet your healthcare needs.

• Returning to Original Medicare and optionally adding a separate Part D prescription drug plan.

It’s important to note that OEP does not apply to those enrolled in Original Medicare only, and you cannot use it to enroll in a Medicare Advantage plan for the first time. This period exists to give current Medicare Advantage plan members flexibility to adjust coverage if their circumstances or healthcare needs change early in the year.

Learn more about the Medicare Advantage Open Enrollment Period.

Other Medicare Enrollment Opportunities

Not everyone’s Medicare enrollment fits neatly into the standard AEP or OEP timeline. Review these options if you missed the AEP or OEP windows or need to make changes outside the usual enrollment periods.

• The Medicare General Enrollment Period: The General Enrollment Period (GEP) runs January 1 to March 31 each year and is for individuals who missed their Initial Enrollment Period (IEP) for Medicare Part B. Coverage begins July 1 of that year, but premiums may be higher due to late enrollment. Learn more about the General Enrollment Period.

• Missing the December 7 AEP Deadline: Missing the AEP deadline doesn’t always mean you must wait a full year to make changes. Certain Special Enrollment Periods (SEPs) may allow you to enroll or switch plans outside of AEP or OEP if you experience qualifying life events, such as moving out of your current plan’s service area or losing your employer coverage. Explore Special Enrollment Periods and qualifying events.

Let SelectQuote Help You Understand Enrollment Windows

All of the terminology and parameters associated with AEP and OEP can be confusing, but our licensed insurance agents can save you time by reviewing your enrollment eligibility. We help you understand the fine print so you can avoid missteps that could impact your health, wallet, or access to care. The service is free, and there’s no obligation to enroll.