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
Quick answer
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 it matters
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.
Continue learning
— suggested by the knowledge graph- Medicare Advantage for veterans: when it makes sense and when it doesn'tCarrier-neutral education on Medicare Advantage (Part C) for retired military — including how MA changes the role of TFL.
- Enrolling in Medicare: timing, methods, and the military-specific rulesWhen and how to sign up for Medicare Parts A and B — and the timing that protects your TRICARE For Life activation.
- Avoiding the Medicare late-enrollment penaltyThe Part B late penalty is permanent — and TRICARE does not waive it. Here's how to make sure you never owe it.
- Annual Election Period (AEP)October 15 – December 7 each year — the main window to join, switch, or drop a Medicare Advantage or Part D plan, with coverage starting January 1.
- Five-Star Special Enrollment PeriodA once-per-year SEP that lets you switch into a CMS-rated 5-star Medicare Advantage or Part D plan available in your area.
- Medicare Advantage Open Enrollment Period (OEP)January 1 – March 31 each year — a one-time chance for current Medicare Advantage enrollees to switch MA plans or drop back to Original Medicare.
- Beneficiary CategoryHow DEERS classifies you (active duty, retiree, family member, survivor, etc.) — determines which TRICARE plans and cost shares apply.
- COBRA After 65COBRA is not creditable coverage for Part B — using it past 65 instead of enrolling in Medicare causes lifetime late penalties.
- Coverage DecisionA formal decision by a Medicare Advantage or Part D plan about whether — and how — it will cover a service, item, or prescription.
- Creditable CoverageNon-Medicare coverage that CMS deems at least as good as a standard Medicare Part D plan — TRICARE Pharmacy qualifies, so TFL beneficiaries don't need Part D.
- Creditable Drug CoveragePrescription drug coverage that CMS certifies is at least as good as standard Medicare Part D — including TRICARE Pharmacy and VA Pharmacy.
- Can I leave Medicare Advantage and go back to Original Medicare + TFL?Yes, during the Annual Enrollment Period (Oct 15 – Dec 7) or the Medicare Advantage Open Enrollment Period (Jan 1 – Mar 31). TFL is waiting whenever you return.
- When can I enroll in or switch Medicare Advantage plans?Annual Enrollment Period (Oct 15 – Dec 7) for next-year coverage. MA Open Enrollment Period (Jan 1 – Mar 31) for one change. Special Enrollment Periods for qualifying life events.
- Will I lose TRICARE For Life if I join Medicare Advantage?No. As long as you keep Medicare Part B, TFL stays. Inside an MA plan, MA becomes primary and TFL becomes a secondary wraparound for in-network MA cost-shares.
- I'm turning 65. What should I do first?About 3 months before your 65th birthday, sign up for Medicare Parts A and B at SSA.gov. TRICARE For Life activates automatically once both are effective and DEERS is current.
- How do I decide between Medicare Advantage and just Original Medicare + TFL?Stay with Original Medicare + TFL if you want maximum provider choice and travel often. Consider MA if you want a Part B giveback, dental/vision/hearing add-ons, and your doctors are in network.
Related glossary terms
Related questions
Related Official Resources
Continue learning straight from the source. Every link below goes to an official government or DoD resource.
Last reviewed January 2026 against the 2026 Medicare & You and TRICARE For Life handbooks.