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Every fall, mailboxes fill up with Medicare Advantage commercials and reminders to «review your options before it’s too late.» Somewhere in that flood of marketing is a real, hard deadline that actually matters: the Medicare Annual Enrollment Period. Here’s exactly when it runs, what you can change, and how to avoid the most common last-minute mistakes.
The Quick Answer
- The next Annual Enrollment Period (AEP) runs October 15 – December 7, 2026
- Any changes you make take effect January 1, 2027
- This is your main annual opportunity to switch Medicare Advantage plans, switch between Medicare Advantage and Original Medicare, or join, switch, or drop a Part D drug plan
- Missing it generally means waiting a full year for your next chance to make these specific changes, unless you qualify for a Special Enrollment Period
What You Can Actually Change During AEP
- Switch from Original Medicare to a Medicare Advantage plan
- Switch from Medicare Advantage back to Original Medicare
- Switch from one Medicare Advantage plan to a different one
- Join, switch, or drop a standalone Part D prescription drug plan
You can make multiple changes during the window — if you switch plans in October and reconsider in November, whichever change you submit last, before December 7, is the one that takes effect. This gives you flexibility to course-correct if you find a better option after your initial decision.
What AEP Does NOT Cover
- Medigap (Medicare Supplement) enrollment. In most states, Medigap policies are only guaranteed-issue during your one-time, 6-month Medigap Open Enrollment Period when you first enroll in Part B — not during AEP. Outside that window, insurers can generally use medical underwriting.
- First-time Medicare enrollment. If you’re new to Medicare, you enroll during your Initial Enrollment Period, a 7-month window centered on your 65th birthday — not AEP.
How to Prepare Before October 15
- Read your Annual Notice of Change (ANOC) letter. Your current plan mails this every September, detailing exactly how your premium, benefits, and network are changing for the coming year. This is often the single most important document in the entire process — many people don’t realize their plan changed until it’s too late.
- Start comparing early. Don’t wait until December. Begin reviewing options in mid-to-late October so you have time to ask questions and avoid a rushed decision.
- Check your specific doctors and medications against any new plan you’re considering — not just the premium or star rating.
- Mark your calendar for both October 15 (when the window opens) and December 7 (the hard deadline).
Common Mistakes to Avoid
- Waiting until the final days. A phone call or mailed form that runs into a snag close to December 7 leaves little room to fix it before the deadline. Enrolling through Medicare’s official Plan Finder tool, calling 1-800-MEDICARE, or contacting the plan directly earlier in the window gives you a much wider safety margin.
- Assuming a mistake can be corrected later through a Special Enrollment Period. SEPs require a specific qualifying event — simply changing your mind after AEP closes generally doesn’t count.
- Ignoring the ANOC letter and assuming your plan stayed the same. Given the broader industry trend of insurers trimming benefits and narrowing networks in recent years, this assumption has caused real problems for people who didn’t realize their coverage had changed.
What Happens If You Miss the Deadline
If you don’t make changes by December 7, your current coverage generally rolls over automatically for the following year — meaning your premiums, doctor network, and drug costs from the prior year continue, unless your plan itself made changes (which is exactly why reading your ANOC matters even if you don’t plan to switch).
If you’re unhappy with your plan after missing AEP, you still have options:
- The Medicare Advantage Open Enrollment Period (January 1 – March 31) gives current Medicare Advantage enrollees one additional chance to switch plans or return to Original Medicare
- A Special Enrollment Period may apply if you experience a qualifying life event — moving, losing employer coverage, or moving in or out of a nursing home are common examples
- The 5-Star Special Enrollment Period (December 8 – November 30) lets you switch into a 5-star-rated plan, if one is available in your area, at any point during the year outside the standard windows
Outside of these specific situations, though, you’ll generally need to wait for the next Annual Enrollment Period.
Frequently Asked Questions
When exactly does the 2026 Annual Enrollment Period run? October 15 through December 7, 2026. Changes made during this window take effect January 1, 2027.
Can I change my mind after making a selection during AEP? Yes — you can make multiple changes during the window itself. Whichever change you submit last, before the December 7 deadline, is the one that actually takes effect.
What if I’m happy with my current plan — do I need to do anything? Not necessarily, but it’s still worth reading your ANOC letter to confirm your plan’s premium, benefits, and network aren’t changing in a way that affects you, since your coverage will otherwise roll over automatically.
Does AEP let me enroll in a Medigap policy? No. Medigap enrollment and guaranteed-issue protections generally follow a separate, one-time 6-month window when you first enroll in Part B, not AEP.
What happens if I miss both AEP and the Medicare Advantage Open Enrollment Period? Unless you qualify for a Special Enrollment Period due to a specific life event, or a 5-star plan is available in your area, you’ll generally need to wait until the next Annual Enrollment Period.
Bottom Line
The Annual Enrollment Period — October 15 to December 7, 2026 — is the single most important date on the Medicare calendar for most beneficiaries. Read your ANOC letter as soon as it arrives in September, start comparing options early rather than waiting until the final days, and remember that missing this window generally means living with your current coverage (or whatever it automatically becomes) for another full year.
Compare your options using the official Medicare Plan Finder, or call 1-800-MEDICARE or your local State Health Insurance Assistance Program (SHIP) for free, unbiased guidance before the deadline.
Disclaimer: Enrollment dates and rules mentioned in this article reflect 2026 CMS guidelines and are confirmed accurate for the described period. Always confirm current details directly with Medicare.gov or 1-800-MEDICARE, since enrollment rules can be updated by CMS.