Open Enrollment vs Annual Enrollment — the 2026 ACA and Medicare timeline
ACA has Open Enrollment. Medicare has the Annual Enrollment Period (AEP) and other windows. They're different programs with different dates — and the names get confused all the time. Here's the full 2026 calendar.
Key takeaways
- ACA Open Enrollment for 2026 coverage: November 1, 2025 – January 15, 2026.
- Medicare AEP (changes for 2026 plans): October 15, 2025 – December 7, 2025.
- Medicare Advantage OEP (one-time MA switch): January 1 – March 31, 2026.
- Outside these windows, you generally need a Special Enrollment Period (SEP) to enroll or switch.
ACA Open Enrollment Period (OEP)
2026 ACA Open Enrollment: November 1, 2025 – January 15, 2026.
During Open Enrollment, anyone can:
- Enroll in a Marketplace health plan for the first time.
- Change carriers or metal tiers (Bronze, Silver, Gold) on their existing plan.
- Add or remove dependents.
- Apply for the Premium Tax Credit (subsidy) and Cost-Sharing Reductions.
Plan effective dates: Plans selected by December 15 start January 1, 2026. Plans selected December 16 – January 15 start February 1, 2026.
Medicare Annual Enrollment Period (AEP)
Medicare AEP: October 15 – December 7 each year. All changes take effect January 1.
During AEP, current Medicare beneficiaries can:
- Switch from Original Medicare to a Medicare Advantage plan, or vice versa.
- Change Medicare Advantage plans (e.g., from a Humana HMO to a UnitedHealthcare PPO).
- Join, switch, or drop a standalone Part D prescription drug plan.
- Drop Medicare Advantage and return to Original Medicare (with optional Medigap, subject to underwriting in most states).
Important: AEP is NOT when you first enroll in Medicare. New beneficiaries use their Initial Enrollment Period (the 7-month window around your 65th birthday).
Medicare Advantage Open Enrollment Period (MA OEP)
MA OEP: January 1 – March 31 each year.
If you're already enrolled in a Medicare Advantage plan as of January 1, you get one chance during this window to:
- Switch to a different Medicare Advantage plan.
- Drop Medicare Advantage and return to Original Medicare (and optionally enroll in a Part D plan).
MA OEP is NOT for people on Original Medicare — only for those starting January 1 in a Medicare Advantage plan. And it's a one-time switch — you can't keep changing throughout the period.
Medicare Initial Enrollment Period (IEP)
IEP: 7 months around your 65th birthday — 3 months before, your birth month, and 3 months after.
This is when you first sign up for Medicare. If your birthday is in May, your IEP runs February through August. The earlier you enroll within the IEP, the earlier coverage starts (typically your birth month if you sign up in the first 3 months).
Missing your IEP without other creditable coverage triggers the Part B late enrollment penalty (a permanent 10% premium increase for every full year delayed).
Medigap Open Enrollment
Medigap OEP: 6 months from your Part B effective date.
This is the one-time window when Medigap (Medicare Supplement) carriers cannot deny you coverage or charge more for health conditions. After this 6-month window, most states allow medical underwriting — meaning carriers can deny you, exclude pre-existing conditions, or charge more.
If you'll ever want a Medigap plan, this is the window to get it.
Quick reference
ACA Open Enrollment: Nov 1 2025 – Jan 15 2026 → for 2026 ACA plans.
Medicare AEP: Oct 15 – Dec 7 2025 → for 2026 MA & Part D plans.
MA OEP: Jan 1 – Mar 31 2026 → one switch for current MA members.
IEP: 7 months around your 65th birthday → first Medicare enrollment.
Medigap OEP: 6 months from Part B effective date → guaranteed-issue Medigap.
Questions about your specific situation?
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