Every fall, more than 65 million Medicare beneficiaries get a narrow window to review their coverage and make changes for the following year. The Medicare AEP, or Annual Enrollment Period, runs from October 15 through December 7, and decisions made during these 54 days determine your healthcare costs and coverage for the entire next calendar year. Missing this window or failing to review your plan’s changes can cost you hundreds or even thousands of dollars.
What Is the Medicare AEP?
The Medicare AEP is the annual open enrollment period established by CMS that allows Medicare beneficiaries to make changes to their Medicare Advantage (Part C) and Medicare Part D prescription drug coverage. It is not the same as the Initial Enrollment Period for new beneficiaries or the Medigap Open Enrollment Period. The AEP specifically governs annual plan switching for existing Medicare enrollees.
During the AEP, any changes you make take effect on January 1 of the following year. If you do not make any changes during the AEP, your current plan automatically renews for the next year with whatever new terms, premiums, and formulary changes your insurer has implemented. This passive renewal is why reviewing your plan annually is so important.
What You Can Do During the AEP
The AEP gives you flexibility to restructure your Medicare coverage in several ways. You can switch from one Medicare Advantage plan to another, join a Medicare Advantage plan for the first time if you are currently on Original Medicare, drop your Medicare Advantage plan and return to Original Medicare, enroll in a standalone Medicare Part D plan, switch from one Part D plan to another, or drop your Part D plan entirely (though this may trigger a late enrollment penalty if you go without creditable drug coverage).
The one thing you cannot do during the AEP is enroll in or change a Medigap supplement plan. Medigap enrollment is governed by separate rules, primarily your initial six-month Open Enrollment Period and any guaranteed-issue rights you may have. For Medigap timing, see our Medicare Enrollment 2025 Guide.
Why You Should Review Your Plan Every Year
Medicare Advantage and Part D plans can change their benefits, premiums, formularies, provider networks, and cost-sharing structures every year. Your plan is required to send you an Annual Notice of Change (ANOC) by September 30, detailing what will change on January 1. Common changes include premium increases of $5 to $30 per month, removal of drugs from the formulary or movement to higher-cost tiers, changes to copay and coinsurance amounts, narrowing or expanding of provider networks, and adjustments to extra benefits like dental, vision, or OTC allowances.
Even if you were satisfied with your plan this year, next year’s version may be significantly different. A drug that was on Tier 2 at a $15 copay might move to Tier 3 at a $47 copay. Your primary care doctor might leave the network. The annual out-of-pocket maximum might increase by $1,000. Reviewing the ANOC and comparing alternatives during the AEP is the only way to catch these changes.
How to Prepare for the Medicare AEP
Start your preparation in September, well before the October 15 start date. Begin by reviewing the ANOC from your current plan. Make a list of all prescription drugs you take, including dosages, and all doctors and specialists you see. Then use the Medicare.gov plan finder to compare your current plan against alternatives in your ZIP code.
When comparing plans, focus on total estimated annual cost rather than just the monthly premium. The plan finder estimates your total drug costs based on the medications you enter. Also check whether your doctors are in each plan’s network and whether your drugs are covered on the formulary at a reasonable tier.
If you are considering switching from Medicare Advantage to Original Medicare during the AEP, understand that you will need to purchase a standalone Part D plan and may want a Medigap supplement plan. However, Medigap enrollment outside your initial OEP may require medical underwriting in most states. This is an important consideration that our Medicare Advantage vs Supplement guide covers in depth.
Common AEP Mistakes to Avoid
The most common mistake is doing nothing. Many beneficiaries let their plans auto-renew without reviewing changes, only to discover higher costs or lost coverage mid-year. Another mistake is focusing only on premiums while ignoring drug formulary changes and network adequacy. A $0-premium plan that does not cover your medications at a reasonable copay is not actually free.
Some beneficiaries also confuse the AEP with the Medicare Advantage Open Enrollment Period (MA OEP), which runs from January 1 through March 31. The MA OEP allows you to make one additional plan change if you are already enrolled in a Medicare Advantage plan. It does not apply to Part D standalone plans or to beneficiaries on Original Medicare.
Finally, do not wait until December 7 to make your decision. Plan selections made in the final days carry a higher risk of processing delays. Aim to complete your enrollment by early to mid-November.
AEP and Prescription Drug Coverage
Drug coverage is often the most important factor to evaluate during the Medicare AEP. The Part D benefit structure for 2026 includes a deductible of approximately $600 (adjusted annually), an initial coverage phase where you typically pay 25 percent of drug costs, and a catastrophic phase where out-of-pocket costs drop to $0 under Inflation Reduction Act provisions that cap annual Part D out-of-pocket spending at $2,000.
If you take expensive brand-name or specialty drugs, the $2,000 annual out-of-pocket cap is a significant benefit. However, which drugs are covered and at what tier varies by plan. Use the Medicare.gov plan finder to enter every drug you take and compare estimated annual costs across available plans. For more on drug coverage costs, see our Part D donut hole article.
Frequently Asked Questions
What happens if I miss the AEP?
If you miss the October 15 to December 7 window, you are generally locked into your current plan until the next AEP, unless you qualify for a Special Enrollment Period due to a qualifying life event. Medicare Advantage enrollees can make one change during the MA OEP from January 1 through March 31.
Can I change my Medigap plan during the AEP?
No. The AEP applies only to Medicare Advantage and Part D plans. Medigap enrollment follows separate rules. You can apply to switch Medigap plans at any time, but outside your initial OEP, medical underwriting may apply. Some states offer annual birthday-rule enrollment. See our Compare Medicare Supplement Plans Guide for details.
Is there a penalty for switching plans during the AEP?
No. There is no penalty for switching plans during the AEP. You can change Medicare Advantage plans or Part D plans as many times as you want during the 54-day window. Only your final election before December 7 takes effect on January 1.
How do I get help comparing plans?
Your State Health Insurance Assistance Program (SHIP) offers free, unbiased counseling from trained volunteers. You can also use the Medicare.gov plan finder, call 1-800-MEDICARE, or work with a licensed insurance agent. Independent agents who represent multiple carriers can compare options side by side at no cost to you.
Can I switch from Original Medicare to Medicare Advantage during the AEP?
Yes. The AEP allows you to join a Medicare Advantage plan if you are currently on Original Medicare. Be aware that once you join Advantage, you should drop any Medigap policy you hold (it is illegal for an insurer to sell you one while you are on Advantage). If you later want to return to Original Medicare with Medigap, underwriting may apply.
Make the AEP Work for You
Treat the Annual Enrollment Period as your annual healthcare financial checkup. Read your ANOC, compare at least three alternative plans, and verify that your doctors and drugs are covered before making a decision. The 54-day window passes quickly, and the choices you make during this period lock in your costs and coverage for an entire year. For a comprehensive view of all enrollment windows and planning strategies, visit our healthcare policy guide and our guide to the last day for Medicare open enrollment.