Medicare OEP vs AEP — Understanding the Key Differences

Medicare enrollment periods can be confusing, and one of the most common misunderstandings is the difference between Annual Enrollment Period (AEP) and Open Enrollment Period (OEP).

While they sound similar, they serve very different purposes.

Annual Enrollment Period (AEP)

October 15 – December 7

AEP is the primary time each year when Medicare beneficiaries can:

• Enroll in or change Medicare Advantage plans

• Enroll in or change Part D prescription drug plans

• Switch between Original Medicare and Medicare Advantage

Changes made during AEP take effect on January 1.

This is when most people first choose or review their Medicare coverage.

Open Enrollment Period (OEP)

January 1 – March 31

OEP is a limited correction window. It is only available to individuals already enrolled in Medicare Advantage.

Key differences:

• Only one change allowed

• No switching from Original Medicare to Medicare Advantage

• Focused on fixing issues discovered after AEP

Why the Difference Matters

Many people assume they can “shop around” during OEP the same way they can during AEP — but that’s not the case.

Making an uninformed decision during OEP can lock you into coverage that doesn’t work for the rest of the year.

Understanding which enrollment period applies to your situation can save you time, money, and frustration.