Medicare Enrollment Periods Explained (IEP, AEP, OEP)

One of the most important things you need to understand as a Medicare agent is when you can actually help someone. Medicare isn't like regular health insurance where clients can sign up whenever they want. There are specific enrollment windows, and if your client misses one, they may have to wait months before they can make a change. Knowing these windows tells you exactly when to reach out, when to take action, and when your hands are tied.

There are four enrollment periods you need to know. The IEP, the AEP, the OEP, and SEPs. Let's go through each one.

The IEP is the Initial Enrollment Period. This is the first time a person becomes eligible for Medicare, and for most people, that happens when they turn 65. The IEP is a seven-month window. It starts three months before the month they turn 65, includes their birthday month, and continues for three months after. So if a client's birthday is in July, their IEP runs from April through October. During this window, they can sign up for Part A, Part B, and choose a Medicare Advantage plan or a standalone Part D drug plan. They can also apply for a Medicare Supplement plan during this time, and this is important because the six-month Medigap open enrollment period starts the first month they have Part B and are 65 or older. During that six-month window, no carrier can turn them down or charge them more based on health history. That guaranteed issue right is something every new agent needs to understand because it directly affects the advice you give.

The AEP is the Annual Enrollment Period. This happens every year from October 15 through December 7. During the AEP, anyone on Medicare can make changes to their coverage. They can switch from Original Medicare to a Medicare Advantage plan. They can switch from one Medicare Advantage plan to another. They can go back to Original Medicare from a Medicare Advantage plan. They can add, drop, or change a Part D prescription drug plan. Changes made during AEP take effect on January 1 of the following year. This is the busiest time of year for Medicare agents. It's when the phones ring, the mailers go out, and clients need help comparing their options for the coming year. If you're going to build a Medicare business, AEP is your season.

The OEP is the Medicare Advantage Open Enrollment Period. This runs from January 1 through March 31 every year. It's specifically for people who are already enrolled in a Medicare Advantage plan. During the OEP, they can switch to a different Medicare Advantage plan or drop their Medicare Advantage plan and go back to Original Medicare. If they drop back to Original Medicare, they can also pick up a standalone Part D drug plan. They can only make one change during this window. The OEP is not a second AEP. It's narrower in scope, but it's an important opportunity for clients who made a choice during AEP that isn't working out.

Finally, there are SEPs, or Special Enrollment Periods. These are triggered by specific life events. A client moves to a new area where their current plan doesn't operate. They lose employer coverage. They qualify for Medicaid or Extra Help. They move into or out of a nursing facility. Each SEP has its own rules and timelines, and the changes a client can make depend on the specific event that triggered it. SEPs are year-round opportunities, and as you gain experience, you'll learn to recognize when a client qualifies for one. For now, just know they exist and that not every enrollment opportunity is tied to AEP.

Here's the simple framework. IEP is when someone first turns 65. AEP is every fall, October 15 through December 7. OEP is the first three months of every year for Medicare Advantage enrollees. SEPs happen when specific life events occur throughout the year.

Your action step is to memorize those four enrollment periods and their timeframes. Know them cold. When a client calls and asks if they can make a change, the first thing you need to know is whether an enrollment window is open for them. That answer determines whether you can help them right now or need to set a follow-up for when the next window opens.

The four Medicare enrollment periods are: the Initial Enrollment Period (IEP), a seven-month window around a client's 65th birthday when they first become eligible for Medicare; the Annual Enrollment Period (AEP), October 15 through December 7, when anyone on Medicare can change coverage for the next year; the Medicare Advantage Open Enrollment Period (OEP), January 1 through March 31, for current Medicare Advantage enrollees to switch MA plans or drop back to Original Medicare; and Special Enrollment Periods (SEPs), which occur year-round when qualifying life events happen.

The Initial Enrollment Period is a 7-month window that starts three months before the month a client turns 65, includes their birthday month, and ends three months after. For example, if a client's birthday is in July, their IEP runs from April through October. During this window, the client can enroll in Part A, Part B, a Medicare Advantage plan, a standalone Part D drug plan, or a Medicare Supplement plan.

The Medicare Annual Enrollment Period (AEP) runs October 15 through December 7 every year, including 2026. During AEP, anyone on Medicare can switch from Original Medicare to a Medicare Advantage plan, change Medicare Advantage plans, drop a Medicare Advantage plan to return to Original Medicare, or add, drop, or change a Part D prescription drug plan. All changes made during AEP take effect on January 1 of the following year.

The Medicare Advantage Open Enrollment Period (OEP) runs January 1 through March 31 every year. It's only for people who are already enrolled in a Medicare Advantage plan at the start of the year. During this window, they can switch to a different Medicare Advantage plan once, or drop Medicare Advantage and return to Original Medicare (and pick up a standalone Part D plan at the same time). Clients can make only one change during the OEP, and it is narrower than the Annual Enrollment Period.

What triggers a Medicare Special Enrollment Period?
Special Enrollment Periods (SEPs) are triggered by qualifying life events. Common triggers include moving to an area outside the current plan's service area, losing employer or union coverage, qualifying for Medicaid or the Extra Help program, moving into or out of a nursing facility or long-term care facility, a plan leaving the Medicare program, and other specific circumstances defined by Medicare. Each SEP has its own rules, timeline, and list of changes the client is allowed to make.