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Medicare AEP: What You Can Change Oct 15–Dec 7 and How to Prepare

Every fall, Medicare gives you 54 days to change your coverage for the coming year. Most people spend those 54 days doing nothing — and a good number of them end up in a plan that no longer fits their doctors, their prescriptions, or their budget. The work that makes AEP go well is not the enrollment itself. It is the hour of preparation you do before October 15. Here is exactly what that hour should look like.

What is the Medicare Annual Enrollment Period?

The Annual Enrollment Period, or AEP, runs from October 15 through December 7 every year. It is the one window when anyone with Medicare can join, drop, or switch a Medicare Advantage plan or a Part D drug plan. Changes you make take effect January 1. Your plan must receive your request by December 7.

You will also hear it called Medicare Open Enrollment or the Fall Open Enrollment Period. Those are three names for the same 54 days. AEP is separate from your Initial Enrollment Period, which is the one-time window around your 65th birthday, and separate again from the Medigap Open Enrollment Period. If the alphabet soup is getting thick, our overview of every Medicare enrollment period lays them out side by side.

The important mental shift is this: AEP is not a renewal deadline. Nothing bad happens if you let it pass. Your current plan simply rolls over into the new year — with whatever changes the insurer has made to it. That is the risk. Doing nothing is not staying put; it is agreeing in advance to next year's version of your plan, sight unseen.

What changes can you actually make between October 15 and December 7?

During AEP you can switch from one Medicare Advantage plan to another, move from Medicare Advantage back to Original Medicare, move from Original Medicare into a Medicare Advantage plan, and join, switch, or drop a standalone Part D drug plan. You may add or drop drug coverage as part of any of those moves.

In practice, that covers almost every combination people ask about. A few notes on the ones that trip people up:

• Dropping Medicare Advantage. If you leave a Medicare Advantage plan and return to Original Medicare, you will generally want a standalone Part D plan, because Original Medicare has no built-in drug coverage.
• Dropping drug coverage entirely. You can. But going more than 63 days without creditable drug coverage can trigger a Part D late enrollment penalty that follows you for as long as you have Part D. This is rarely worth it just to save a small premium.
• Changing your mind mid-window. If you submit more than one enrollment request during AEP, the most recent one generally supersedes the earlier ones. You are not locked in by an early October decision.

What can't you change during AEP?

AEP does not apply to Medicare Supplement (Medigap) plans. You may apply for a Medigap policy any time of year in Arizona, but outside your one-time six-month Medigap Open Enrollment Period or a federal guaranteed issue right, an insurer may review your health history and decline you or charge more.

This surprises people every October, and it is the single most expensive misunderstanding in the fall. A Medicare Advantage plan must take you regardless of health during AEP. A Medicare Supplement plan does not have to. So the move from Original Medicare plus Medigap into a Medicare Advantage plan is usually easy to make and sometimes very hard to reverse.

Arizona does not have a "birthday rule" giving residents an annual window to change Medigap plans without underwriting. We covered how that works, and what it means for choosing a plan letter in the first place, in our comparison of Medigap Plan G vs Plan N in Arizona. The practical rule for AEP: if you currently hold a Medigap policy you are happy with, do not cancel it in order to try something else until the something else is approved and in force.

AEP also does not change your Part A and Part B enrollment, your Part B premium, or any income-related premium adjustment. Those run on separate tracks.

How should you prepare before October 15?

Gather four things: your Annual Notice of Change letter, a current list of your prescriptions with doses, a list of the doctors and hospitals you actually use, and your preferred pharmacy. With those four in hand, comparing plans takes minutes instead of hours, and you stop guessing.

1. Read the ANOC. Your Medicare Advantage or Part D plan must deliver its Annual Notice of Change to you by September 30. It is the document that tells you what is changing on January 1 — premium, deductible, copays, out-of-pocket maximum, drug tiers, and network. It arrives in a fat envelope alongside the Evidence of Coverage, which is why so many go straight into the recycling. The ANOC is the short one. Keep it.

2. Write down your drugs exactly. Name, dose, and how often. Generic substitutions and dosage changes over the year are common, and a plan comparison built on last year's list gives you last year's answer. Drug coverage is where most of the real money moves — a plan can cover your medication one year and move it to a higher tier, or off its list entirely, the next.

3. List your providers, including the ones you saw once. Your cardiologist, your dermatologist, the imaging center your doctor refers to. Networks change between plan years, and a network that fits your primary care physician but not your specialist is not a fit.

4. Note your pharmacy. Many drug plans have preferred and standard pharmacies, and the same prescription can cost different amounts at each. If you fill at a particular location in Oro Valley or Green Valley because it is close, check that it is preferred under the plan you are considering.

5. Only then compare plans. The official comparison tool at Medicare.gov lets you enter your drug list and see estimated annual costs across every plan available in your ZIP code. Estimated annual cost — not premium — is the number that matters. We walk through why in our look at $0-premium Medicare Advantage plans in Pima County.

What should Tucson and Pima County residents check specifically?

Check hospital networks first. Pima County's major systems — TMC Health, Banner – University Medicine, Northwest Healthcare, and Carondelet — do not all participate in every Medicare Advantage plan, and participation can change from one plan year to the next. Confirm your hospital and your specialists for the 2027 plan year, not the current one.

This is the most local, most consequential item on the list, and it is the one people assume they can skip. A plan that covered your cardiologist at one system in 2026 may not in 2027, and the plan is not obligated to call you about it. Our guide to which Tucson hospital systems work with your Medicare plan explains how HMO, PPO, and Medigap access differ, and how to verify a provider before you enroll rather than after.

Two more items worth attention this particular fall:

• Part D numbers are moving. For 2027, the most a Part D plan may charge as an annual deductible rises to $700, up from $615 in 2026. The annual cap on what you pay out of pocket for covered Part D drugs rises to $2,400, up from $2,100. Plans may set a lower deductible than the maximum, so your ANOC is the authority on what your plan will actually charge.
• Snowbird and part-year travel. If you spend part of the year outside Arizona, ask how the plan handles care away from home. Rules vary a great deal between plan types, and it is a poor thing to discover in an emergency room in another state.

What if you change your mind after December 7?

You have limited second chances. If you are in a Medicare Advantage plan on January 1, the Medicare Advantage Open Enrollment Period from January 1 through March 31 lets you make one change — to a different Medicare Advantage plan, or back to Original Medicare with a standalone drug plan.

That window does not let you switch standalone Part D plans on their own. Separately, Medicare allows a one-time Special Enrollment Period to move into a plan rated five stars, if one is offered where you live. Certain life events — moving out of your plan's service area, losing employer or retiree coverage, qualifying for Extra Help — also open Special Enrollment Periods outside the fall window.

None of these fully substitute for getting the fall decision right, because none of them reopen the Medigap door. Treat January through March as a correction mechanism for Medicare Advantage, not as a reason to be casual in November.

Frequently Asked Questions

Do I have to do anything during Medicare AEP if I like my plan?

No. If you take no action, your current plan renews automatically on January 1 with whatever changes it has announced. But renewing is a decision, not a default. Read your Annual Notice of Change first, so that you are renewing on purpose rather than by accident. Plenty of people review their ANOC, find nothing troubling, and stay put — that is a good outcome, reached deliberately.

Can I change my Medicare Supplement plan during AEP?

Not through AEP. The October 15 to December 7 window applies to Medicare Advantage and Part D plans only. You may apply for a Medigap plan at any time of year in Arizona, but outside your one-time Medigap Open Enrollment Period or a guaranteed issue right, the insurer may use medical underwriting and can decline you or charge more.

What if I enroll in a plan during AEP and then change my mind?

You have some room to correct course. Within AEP itself, a later request generally replaces an earlier one. After January 1, if your coverage is a Medicare Advantage plan, the Medicare Advantage Open Enrollment Period from January 1 through March 31 allows one switch — to a different Medicare Advantage plan or back to Original Medicare with a separate drug plan.