Glossary
AEP & OEP (Election Periods)
AEP (Oct 15 – Dec 7) is when you can join, switch, or drop MA plans. OEP (Jan 1 – Mar 31) lets you change MA plans once.
Also known as: Annual Election Period, Open Enrollment Period
What is it?
AEP runs October 15 to December 7 — the main annual window to join, switch, or drop a Medicare Advantage or Part D plan. OEP runs January 1 to March 31 — gives MA enrollees one chance to switch plans or return to Original Medicare.
Why does it matter?
If a plan stops being a good fit (network change, formulary change, doctor leaves), these are your windows to fix it.
When you'll encounter it
Annually.
Impact on Medicare
Doesn't change Original Medicare itself.
Impact on TRICARE For Life
TFL stays the same regardless of which window you use.
Impact on Medicare Advantage
These are the windows in which MA decisions can be made.
Common misconceptions
- "I can switch MA plans any time." — Only during AEP, OEP, or a qualifying SEP.
Related glossary terms
Related questions
Official sources
Last reviewed January 2026 against the 2026 Medicare & You and TRICARE For Life handbooks.