Medicare Open Enrollment Period
AEP vs. OEP
When You Can Change Coverage

What is Medicare AEP and when does it run?

Medicare AEP runs from October 15 through December 7 each year. AEP is commonly called the Annual Enrollment Period. In CMS enrollment guidance, the formal term is the Annual Election Period, while Medicare.gov refers to the same October 15 through December 7 window as the Open Enrollment Period.

For 2026 planning, AEP runs from October 15, 2026 through December 7, 2026. Changes made during this period generally take effect January 1, 2027, as long as the plan receives the enrollment request by December 7. AEP is used to make Medicare Advantage and Part D prescription drug coverage changes. It is not the same as the Initial Enrollment Period for first signing up for Medicare Part A and Part B.

What coverage changes can you make during AEP?

What you can do during AEP depends on the coverage you have now, but the period generally allows several common changes:

• Switch from Original Medicare to a Medicare Advantage Plan, if you meet the plan eligibility requirements.
• Switch from a Medicare Advantage Plan back to Original Medicare.
• Switch from one Medicare Advantage Plan to another, with or without drug coverage.
• Join, switch, or drop a Medicare drug plan, also called Part D, when the Medicare enrollment rules allow it.
• Add or drop drug coverage when changing certain Medicare Advantage options.

If you switch to Original Medicare, you may need to consider whether you also want separate Part D drug coverage. Medicare Supplement Insurance, often called Medigap, has separate enrollment rules. AEP does not by itself guarantee that you can buy any Medigap policy you want.

When do AEP changes start?

Changes made during AEP generally start on January 1 of the next year, as long as the plan gets your enrollment request by December 7.

If you switch from one Medicare drug plan to another, your old drug coverage generally ends when the new drug coverage begins. Medicare says you should get a letter from your new plan telling you when coverage begins.

What is Medicare Advantage OEP and how is it different?

The Medicare Advantage Open Enrollment Period (OEP) runs from January 1 through March 31 each year for people who are already enrolled in a Medicare Advantage Plan. Unlike AEP, OEP is not a general enrollment period for everyone with Medicare.

During OEP, you can make one change: switch to another Medicare Advantage Plan, with or without drug coverage, or leave Medicare Advantage and return to Original Medicare. If you return to Original Medicare, you can also join a stand-alone Part D prescription drug plan. A change made during OEP generally takes effect on the first day of the month after the plan receives your request.

If you have Original Medicare, you cannot use the Medicare Advantage OEP to join a Medicare Advantage Plan, join a stand-alone Part D plan, or switch from one stand-alone Part D plan to another. Medicare also provides a Medicare Advantage Open Enrollment opportunity during the first 3 months a newly eligible person has both Part A and Part B if that person enrolled in Medicare Advantage.

Can you change Medicare coverage outside AEP or OEP?

Sometimes. Medicare allows Special Enrollment Periods for certain life events, such as moving, losing or changing other coverage, becoming eligible for Medicaid, getting Extra Help, or other qualifying circumstances. The type of change you can make and the timing depend on the specific event.

Because Special Enrollment Period rules are situation-specific, it is important to verify whether your event qualifies before assuming you can change plans. A Special Enrollment Period can provide a separate opportunity to make a coverage change outside the normal AEP or Medicare Advantage OEP windows.

What should you know about Medigap before switching?

Medigap is private supplemental insurance that helps pay some out-of-pocket costs in Original Medicare. It is different from Medicare Advantage and Part D.

Medigap has its own enrollment protections. Under federal rules, your Medigap Open Enrollment Period generally lasts 6 months and starts the first month you have Medicare Part B and are 65 or older. This one-time Medigap enrollment period is different from both AEP and the Medicare Advantage OEP and does not repeat every year.

If you plan to leave Medicare Advantage for Original Medicare during AEP or OEP, check Medigap rules before making the change. AEP and OEP do not by themselves create a general federal guaranteed issue right to buy any Medigap policy. Depending on your situation and state rules, you may not have a guaranteed right to buy every Medigap policy.

Official Sources