Medicare Annual Enrollment Period 2026: What You Can (and Can't) Change

Medicare's Annual Enrollment Period (AEP) runs October 15 through December 7 each year. Changes take effect January 1. It's the main window to switch Medicare Advantage or Part D plans — but it does not give you an annual right to change Medigap coverage. Here's how to use it correctly.

What AEP is — and isn't

The Annual Enrollment Period (also called Medicare Open Enrollment) runs October 15 – December 7 each year. Any changes you make take effect January 1 of the following year. The period exists primarily to let Medicare enrollees re-evaluate their Part D drug plans and Medicare Advantage plans as plan offerings, premiums, and drug formularies change annually.¹

AEP is not the same as:

• Initial Enrollment Period (IEP) — the 7-month window around your 65th birthday when you first enroll in Medicare. See Medicare enrollment timeline.
• Special Enrollment Period (SEP) — triggered by qualifying life events (job loss, moving out of a plan's service area, etc.). See Medicare at 65 while still working for the employer-coverage SEP.
• Medigap Open Enrollment Period — your one-time 6-month window starting when you enroll in Part B at age 65. That window closed. AEP doesn't reopen it. See Medigap guaranteed issue rights.

What you CAN do during AEP

If you're already enrolled in Medicare (any coverage type), during AEP you may:

• Switch from one Medicare Advantage plan to another. New plan's benefits, network, and premiums take effect January 1.
• Switch from Medicare Advantage to Original Medicare. You'll return to Part A + Part B coverage — and you'll likely want to add a Part D drug plan (your MA plan's drug coverage does not transfer). If you want Medigap, you'll need to apply and may be subject to underwriting (except in guaranteed-issue states or situations — see below).
• Switch from Original Medicare to Medicare Advantage. This bundles your hospital, medical, and usually drug coverage into one plan. Your existing Medigap policy becomes useless once you enroll in MA — it can't be used alongside an MA plan.
• Join or switch a standalone Part D drug plan (if you're in Original Medicare or have an MA-only plan without drug coverage).
• Drop Part D drug coverage entirely (rarely wise — you may owe a late enrollment penalty if you go without creditable coverage and rejoin later).

What you CANNOT do during AEP

Switch Medigap plans. There is no annual right to change Medigap supplemental coverage. In most states, if you want to switch from Plan G to Plan N, or from one insurer's Plan G to a cheaper insurer's Plan G, you must apply and pass medical underwriting. The insurer can deny you or charge more based on health conditions.

Exceptions exist, but they are limited. See the full rules in Medigap guaranteed issue rights:

• A few states (New York, Connecticut, Massachusetts) allow year-round Medigap enrollment without underwriting.
• About 14 states have "birthday rules" giving you a 30–60 day window around your birthday each year to switch to an equal or lesser plan without underwriting.
• If you're switching from Medicare Advantage back to Original Medicare and you enrolled in MA within the last 12 months, you have a federal Medigap guaranteed-issue right.

Part D: why AEP matters every year for high-income retirees

Part D plans change annually. Drug formularies shift (a drug in Tier 2 this year may move to Tier 4 next year), plan premiums change, and pharmacy networks change. During AEP, Medicare's Plan Finder tool at medicare.gov shows you exactly which plan covers your drugs at the lowest total cost for the coming year. Switching is worth doing whenever your total annual drug costs would be significantly lower under a different plan.

For high-income enrollees, IRMAA surcharges are added to Part D premiums on top of the plan's own premium. In 2026, Part D IRMAA surcharges range from $14.50/month (Tier 1) to $91.00/month (Tier 5) per person.² The surcharge applies to every Part D plan at the same tier — switching plans doesn't reduce IRMAA. But your IRMAA tier is based on income from two years prior, so if your income dropped recently, you may qualify for a lower tier next year (or an immediate reduction via SSA-44 appeal).

The MA Open Enrollment Period: January 1 – March 31

AEP isn't the only window. If you're already enrolled in a Medicare Advantage plan, you get a second opportunity each year: the Medicare Advantage Open Enrollment Period (MA OEP), which runs January 1 – March 31. During this window, you can:³

• Switch from one MA plan to another MA plan (one change only during this period).
• Switch from Medicare Advantage back to Original Medicare and join a standalone Part D plan.

What the MA OEP does not allow: switching from Original Medicare to MA (that's AEP or SEP only), or enrolling in a new Part D plan if you're already in Original Medicare without MA. Changes made during the MA OEP take effect the first day of the following month.

The MA OEP is valuable if you enrolled in a new MA plan during AEP and quickly discovered a network or coverage problem. You don't have to wait a full year — you have until March 31 to correct the decision.

AEP checklist for high-income retirees

Each fall before December 7, review:

1. Your Annual Notice of Change (ANOC). Plans must mail this by September 30 each year. It shows your plan's premiums, deductibles, copays, and drug formulary changes for the coming year. If anything meaningful changed, shop alternatives during AEP.
2. Your drug formulary. Use Medicare's Plan Finder to compare total out-of-pocket drug costs across available plans. The cheapest plan for your specific drug list in 2026 may differ from 2025.
3. Your IRMAA tier for next year. Your 2026 income will determine your 2028 IRMAA. But your 2024 income (already on file with SSA) determines your 2026 IRMAA. If your income dropped materially in 2024 or 2025, check whether you qualify for an SSA-44 appeal before AEP ends — a successful appeal can lower your Part D premiums immediately.
4. Your MA network. Did your doctors stay in-network? Did the plan's service area change? Network disruptions are one of the most common triggers for AEP switches.
5. The one-way door risk before switching. If you're thinking about moving from Original Medicare + Medigap to MA because of premium savings, model what happens if you want to switch back. In most states, you cannot get Medigap coverage again without underwriting. A specialist can run the long-term cost comparison — including expected out-of-pocket costs under each scenario at different health utilization levels.

Sources

1. Medicare.gov: Open Enrollment — authoritative AEP dates (October 15–December 7) and what changes are allowed. Values verified May 2026.
2. CMS: 2026 Medicare Parts A & B Premiums and Deductibles — Part B base premium $202.90; full IRMAA surcharge schedule including Part D add-ons.
3. Medicare.gov: Joining a Plan — MA Open Enrollment Period (January 1–March 31) rules and one-change limitation.
4. CMS: 2026 Medicare Advantage & Part D Landscape State-by-State Fact Sheet — plan availability and stability overview for 2026.

Medicare enrollment period rules and IRMAA surcharge amounts verified against CMS and Medicare.gov as of May 2026. Medicare rules and premiums change annually; verify current-year figures before acting.