Medicare Annual Enrollment Period: Dates, Deadlines, and What You Can Change

Every fall, mailboxes and inboxes fill up with Medicare Advantage commercials, colorful brochures, and reminders to “review your options before it’s too late.” Somewhere in that flood of marketing is a real deadline that matters: the Medicare Annual Enrollment Period. This is the main window nearly every Medicare enrollee gets each year to change Medicare Advantage and Part D drug coverage, and missing it usually means waiting another twelve months for the next chance. Here’s what the Annual Enrollment Period actually covers, when it opens and closes in 2026, and how to get ready without the last-minute scramble.

State Health Insurance Assistance Program (SHIP) counselors hear a version of the same story every January: someone let their Medicare Advantage plan renew automatically in December, only to find that a longtime specialist was no longer in network or that a routine prescription jumped from a small copay to an unexpectedly large one. Nothing about that means the enrollee did anything wrong. Plans are allowed to change their networks, drug formularies, and costs every year, and the Annual Enrollment Period is the one structured chance to catch those changes before they take effect, not after.

What Is the Medicare Annual Enrollment Period?

• The Annual Enrollment Period (AEP) is also called Medicare Open Enrollment or the Annual Election Period. All three names refer to the same window.
• It’s set by the Centers for Medicare & Medicaid Services (CMS), the federal agency that runs Medicare, and it happens on the same dates every year, nationwide.
• AEP is the main opportunity for people already on Medicare to change Medicare Advantage (Part C) coverage or Medicare prescription drug (Part D) coverage for the year ahead.
• It’s different from the enrollment period that applies when someone first becomes eligible for Medicare, and different from the shorter window available only to current Medicare Advantage members early each year. Both are covered further down.

When Is AEP 2026? Key Dates to Mark

• AEP runs October 15 through December 7, 2026.
• Any changes made during this window take effect January 1, 2027.
• The plan needs to receive the enrollment request by December 7. Requests mailed close to the deadline can cut it close, so enrolling through Medicare’s official plan comparison tool, calling 1-800-MEDICARE, or contacting the plan directly earlier in the window leaves a wider safety margin.
• Multiple changes are allowed during AEP. If a decision is made in October and reconsidered in November, the change submitted last, before December 7, is the one that takes effect.

What You Can Change During AEP

• Join a Medicare Advantage plan for the first time, if not already enrolled in one.
• Switch from one Medicare Advantage plan to another, with or without drug coverage.
• Switch from Original Medicare to a Medicare Advantage plan.
• Switch from a Medicare Advantage plan back to Original Medicare, with the option to also join a standalone Part D drug plan.
• Join a Medicare Part D drug plan, if not currently enrolled in one.
• Switch from one Part D plan to another.
• Drop Part D drug coverage entirely.

What AEP Doesn’t Cover

• First-time Medicare enrollment. Someone turning 65 generally enrolls during their own seven-month Initial Enrollment Period, described below, not AEP.
• Buying or switching a Medicare Supplement Insurance (Medigap) policy. Medigap enrollment generally works on a different set of rules, and coverage outside a person’s own Medigap Open Enrollment Period or a qualifying event may involve medical underwriting. A licensed insurance professional or SHIP counselor can help sort out what options may be available for a specific situation.
• A second chance later in the year for everyone. AEP is often confused with the Medicare Advantage Open Enrollment Period, a separate window from January 1 through March 31 that only applies to people already in a Medicare Advantage plan and allows just one additional change.

Common Mistakes During AEP

• Assuming no letter means no changes. Plans send the Annual Notice of Change every September, but it’s easy to skim past or set aside, and even small formulary or network changes can matter for a specific medication or doctor.
• Comparing plans on premium alone, without checking whether current doctors and pharmacies are still in network or whether a specific medication is still covered at the same cost.
• Waiting until the final days of the window to enroll. A call to the plan or a mailed form that runs into a snag close to December 7 leaves little room to fix it before the deadline.
• Assuming a missed decision can be corrected later through a Special Enrollment Period. Outside a qualifying life event, AEP is generally the main chance until the following January’s Medicare Advantage Open Enrollment Period, which allows only one change and only for people already in a Medicare Advantage plan.
• Overlooking continuity of care for an ongoing health condition. A plan that looks appealing on paper may still involve a gap in coverage for specialists tied to a chronic condition, which is worth checking closely before switching.

How to Get Ready Before AEP Opens

• Read the Annual Notice of Change (ANOC) letter that arrives from the current plan every September. It outlines what’s changing about the plan’s costs, coverage, and provider network for the coming year.
• Make a current list of prescriptions, dosages, and the pharmacies used. Formularies (the list of medications a plan covers) can shift from year to year, even for a plan that otherwise stays about the same.
• Confirm which doctors, specialists, and hospitals matter most, and check whether they’re in a plan’s network before enrolling.
• Compare plans using Medicare’s official plan comparison tool, entering medications and preferred pharmacies for a personalized cost estimate. Senioridy’s step-by-step guide to using the Medicare Plan Finder walks through the tool from start to finish.
• For a closer look at how to weigh plan options side by side, Senioridy’s guide to choosing and switching Medicare Advantage plans covers the comparison factors that tend to matter most.
• Contact a local State Health Insurance Assistance Program (SHIP) counselor for free, unbiased guidance. SHIP counselors aren’t affiliated with any insurance company or plan.

What Happens After Enrolling

• The new plan generally sends a confirmation and a new member ID card before the new coverage starts.
• Coverage from a change made during AEP begins January 1 of the following year, regardless of when during the window the request was submitted.
• Once December 7 passes, AEP closes for the year. Other enrollment windows may still apply after that date, described next.

Other Enrollment Windows Worth Knowing About

• Medicare Advantage Open Enrollment Period (January 1 through March 31): available only to people already enrolled in a Medicare Advantage plan. It allows one additional change, either to a different Medicare Advantage plan or back to Original Medicare with a standalone Part D plan.
• Special Enrollment Periods (SEPs): triggered by specific life events like moving, losing other coverage, or qualifying for Medicaid or Extra Help. Senioridy’s guide to Medicare Advantage Special Enrollment Periods covers the most common SEP triggers and how long each window generally stays open.
• Initial Enrollment Period (IEP): the seven-month window centered on someone’s 65th birthday month, for first-time Medicare enrollment.

Getting Help

• 1-800-MEDICARE (1-800-633-4227; TTY users can call 1-877-486-2048) is available year-round for enrollment questions.
• Local SHIP counselors, reachable through the national SHIP directory, offer free one-on-one guidance and aren’t tied to any insurance company.

The Bottom Line

The Annual Enrollment Period only comes around once a year, but reviewing coverage doesn’t have to wait until October. Comparing options ahead of time and knowing the key dates turns AEP from a scramble into a straightforward decision. Families weighing whether a loved one’s current living situation still fits their needs can also browse Senioridy’s directory of in-home senior care providers to compare local options.

This article is for informational purposes only and does not constitute legal, financial, or medical advice. Enrollment dates and plan details are subject to change; confirm current requirements with official program representatives. Medicare Advantage plan rules may differ from Original Medicare in ways that matter for a specific situation. For free, personalized Medicare guidance, contact your State Health Insurance Assistance Program (SHIP) counselor at shiphelp.org, available in every state at no cost.