Medicare Enrollment Periods happen on a rolling basis throughout the year. Some of them are triggered by specific events such as turning 65 or a significant life change. Others—such as the Annual Enrollment Period (AEP)—open up in the same time frame each calendar year.

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Some types of changes to Medicare coverage are available year-round, but other changes need to be made during these specific windows of time known as enrollment periods. Some of these enrollment periods have similar-sounding names or overlapping dates, so it can be tricky to understand exactly what is available and when.

We know how confusing it can get for Medicare shoppers and enrollees to figure out which plans are available to them at any given time, so we made a guide to help you figure it all out. Here is our yearly guide to what plans you can access and when:

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1. Annual Enrollment Period (AEP) for Medicare Advantage plans and Medicare Part D

The Annual Enrollment Period (AEP) occurs from October 15-December 7 each calendar year. During this time, people who are already enrolled in Medicare can re-evaluate their coverage and make changes. Some of the most common changes include adding or switching Medicare Advantage plans, dropping from a Medicare Advantage plan to Original Medicare and switching, dropping or adding Medicare Part D prescription drug plans.

After making changes during AEP, your new coverage begins January 1st of the following year. 

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2. General Enrollment Period (GEP) for Original Medicare

The General Enrollment Period (GEP) takes place each calendar year from January 1st to March 31st. During the GEP, it’s possible to enroll in Original Medicare outside of either your Initial Enrollment Period (IEP) or an Special Enrollment Period (SEP) triggered by a life event. During the GEP, signing up for a Medicare plan means your coverage won’t begin until July 1st. Because of this, GEP can be considered a “last resort” way to sign up for Medicare.

3. Initial Enrollment Period (IEP)

The Initial Enrollment Period (IEP) is a once-in-a-lifetime event triggered by turning 65. This enrollment period begins three months before turning 65, during the enrollee’s birthday month, and ends three months after turning 65. If you are receiving Social Security benefits, you will be automatically enrolled in Original Medicare. If not, you can use the IEP to sign up during this seven-month window.

Enrolling during the IEP also avoids any late fees associated with not having Medicare coverage. However, it is possible to delay the start of Medicare Part B without a penalty if you’re covered by another type of creditable coverage plan, such as employment-based insurance.

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4. Open Enrollment Period (OEP) for Medicare Advantage

The Medicare Advantage Open Enrollment Period (MA-OEP) occurs between January 1st and March 31st of each calendar year. During the MA-OEP, it is possible to make one change to your Medicare Advantage coverage. This enrollment period applies only to people who already have a Medicare Advantage plan. 

The change to your Medicare Advantage plan can be switching to a new Medicare Advantage plan if one you like better is offered in your area, or dropping from Medicare Advantage to Original Medicare only instead. If you choose to drop a Medicare Advantage plan, the MA-OEP will also allow you to also sign up for a standalone Medicare Part D plan.

5. Special Enrollment Period (SEP)

Special Enrollment Period (SEP) is a window of time when it’s possible to enroll in Original Medicare or a Medicare Supplement plan outside of the normal times in the calendar year when those options are available and outside your IEP (see above). 

For Original Medicare, losing employment-based coverage grants an 8-month SEP to sign up for Medicare Parts A and B. 

For private insurance plans like Medicare Advantage or Part D plans, events that might trigger an SEP include moving out of your plan’s coverage area, involuntary loss of coverage, or qualifying for government assistance such as Medicaid or Extra Help. The intent of an SEP is to make coverage changes when your health coverage is impacted by life circumstances, so other unusual events such as natural disasters may qualify you in some cases. 

If an SEP is triggered, it can be a good time to take another look at all available options for Original Medicare, Medicare Supplement insurance plans, and Medicare Advantage plans going forward.