Glossary
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.
Also known as: MA-OEP, MAOEP, MA Open Enrollment, Medicare Advantage OEP
Quick answer
The Medicare Advantage Open Enrollment Period runs January 1 through March 31 every year. Only people already enrolled in a Medicare Advantage plan as of January 1 can use it — and only ONCE. You may switch to a different MA plan, or drop MA and return to Original Medicare (with the option to add a stand-alone Part D plan).
Why it matters
OEP is the safety valve after AEP. If your new plan year starts on January 1 and your doctor isn't in network, a medication isn't on the formulary, or the giveback evaporated — OEP lets you fix it without waiting a full year.
Why this matters at age 65
For a TFL beneficiary who joined an MA plan and immediately discovered it doesn't fit, OEP is the exit door. Drop back to Original Medicare; TFL resumes as a full secondary payer with no copays at Medicare-participating providers.
When you'll encounter it
January 1 through March 31, if you're enrolled in an MA plan on January 1.
Impact on Medicare
Switching plans changes how your Medicare benefits are delivered. Returning to Original Medicare puts you back under traditional A and B coverage with full provider choice.
Impact on TRICARE For Life
Crucial: dropping MA returns TFL to its full secondary-payer role at any Medicare-participating provider. TFL never changes — but what it supplements does.
Impact on Medicare Advantage
You can switch to ONE other MA plan during OEP, or drop MA entirely. You cannot switch from Original Medicare INTO an MA plan during OEP — that's an AEP-only move.
Military-specific context
Many veterans who try MA discover after a few months that they preferred Original Medicare + TFL's nationwide flexibility. OEP exists precisely for that course-correction.
Common misconceptions
- "OEP is when I can drop Original Medicare to join MA." — No — OEP is only for people already in an MA plan. To join MA from Original Medicare, use AEP or IEP.
- "I can make unlimited changes during OEP." — You get one change. After that, you're locked in until next AEP unless an SEP applies.
Common mistakes to avoid
- Dropping MA without confirming TRICARE Pharmacy is still your active drug coverage (it is — TRICARE never changes).
- Confusing OEP with AEP and missing the March 31 deadline.
- Trying to use OEP to join MA from Original Medicare — not allowed.
Real-world scenario: A retired Marine joined an MA plan during AEP and discovered in February that his cardiologist is out of network.
Uses OEP to drop back to Original Medicare effective March 1. TFL immediately resumes paying as full secondary for the cardiologist. Stays on Original Medicare until next AEP when he re-evaluates.
What should I do?
- 1Use the first 60 days on a new MA plan to test it — verify doctors, pharmacies, and medications.
- 2If something doesn't fit, file the change before March 31 — coverage starts the first of the following month.
- 3When dropping MA, confirm Original Medicare and TFL are coordinating on your first post-OEP claim.
- 4If you keep MA, set a calendar reminder for the next AEP (October 15) to re-evaluate.
Questions people commonly ask
- Can I switch MA plans whenever I want?
- How is OEP different from AEP?
- If I drop MA, does TFL come back automatically?
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.
- 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.
- 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.
- What is the 5-star Special Enrollment Period?A one-time-per-year chance (Dec 8 – Nov 30) to switch into a 5-star-rated Medicare Advantage or Part D plan in your area, outside the normal enrollment windows.
- 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.
Related glossary terms
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.