Medicare Annual Enrollment Period (AEP): Your Complete 2026 Guide

The Annual Enrollment Period gives you the opportunity to make specific changes to your Medicare coverage. These changes all take effect on January 1 of the following year, regardless of when during the AEP window you make them.

You can switch from one Medicare Advantage plan to another Medicare Advantage plan. This is the most common AEP action. If your current MA plan is raising premiums, narrowing its network, removing your doctors, or changing drug coverage for 2027, you can move to a different plan that better fits your needs.

You can switch from one standalone Part D prescription drug plan to another. Drug plan formularies change every year, and a medication that was Tier 2 this year might move to Tier 3 or be removed entirely. Comparing Part D plans annually is one of the most impactful things you can do to control costs.

You can drop your Medicare Advantage plan and return to Original Medicare (Parts A and B). If you make this switch, you can also enroll in a standalone Part D plan at the same time. However, you will not have guaranteed issue rights to purchase a Medigap plan, which means you may face medical underwriting.

You can join a Medicare Advantage plan if you are currently on Original Medicare. Your MA plan will replace your Part A and Part B coverage and typically includes Part D drug coverage built in.

You can enroll in a standalone Part D plan for the first time if you have been on Original Medicare without drug coverage. Be aware that if you went more than 63 consecutive days without creditable drug coverage, you may owe a Part D late enrollment penalty.

AEP is not a universal open season for all Medicare decisions. Several important actions cannot be taken during this window.

You cannot enroll in Medicare Part A or Part B for the first time during AEP. Initial enrollment happens during your Initial Enrollment Period (the 7-month window around your 65th birthday) or the General Enrollment Period (January 1 to March 31 each year).

You cannot switch Medigap (Medicare Supplement) plans with guaranteed issue rights during AEP. Medigap enrollment is governed by its own rules. Your guaranteed issue period is the 6-month window that starts when your Part B begins. Outside that window, insurers can use medical underwriting and may deny your application based on health conditions.

You cannot drop Medicare coverage entirely during AEP. If you want to disenroll from Part B, that is a separate process handled through Social Security.

You cannot use AEP to enroll in an employer group health plan or COBRA. Those are governed by separate enrollment rules tied to your employment status.

September 2026: Your current Medicare Advantage or Part D plan mails you an Annual Notice of Change (ANOC) letter. This document details every change to your plan for 2027, including premium changes, formulary updates, network modifications, and benefit adjustments. Read this letter carefully.

October 1, 2026: The Medicare Plan Finder tool at Medicare.gov updates with all 2027 plan options. You can begin comparing plans, checking drug formularies, and verifying provider networks for the upcoming year.

October 15, 2026: AEP officially opens. You can now make plan changes. There is no advantage to changing on the first day versus the last day. All changes take effect January 1, 2027 regardless of when you submit them.

December 7, 2026: AEP closes at 11:59 PM in your local time zone. After this deadline, you cannot make changes until the next enrollment period (either the Medicare Advantage Open Enrollment Period in January through March, or the next AEP in October 2027).

January 1, 2027: All AEP changes take effect. Your new plan, new premiums, new formulary, and new network are now active.

Not reading your ANOC letter. This is the single biggest mistake. Your plan can change premiums, drop drugs from its formulary, remove doctors from its network, and alter cost-sharing, all without your explicit consent. If you do not read the ANOC, you will not know what changed until you get an unexpected bill in January.

Assuming your plan is the same year to year. Medicare Advantage and Part D plans are re-filed with CMS annually. Even if the plan name stays the same, the benefits, costs, and network can change significantly. A plan that was excellent in 2026 may not be the best option for 2027.

Missing the December 7 deadline. AEP is a hard deadline. If you miss it, your next opportunity to make changes is the Medicare Advantage Open Enrollment Period (January 1 to March 31), which only allows you to switch MA plans or drop MA to Original Medicare. It does not allow standalone Part D changes.

Not checking your drug formulary. Even if your plan's premium stays the same, your drug costs can change dramatically if medications move to higher tiers or are removed from the formulary entirely. Always run your medications through the Medicare Plan Finder to compare total annual costs.

Dropping MA without understanding Medigap underwriting. If you drop your Medicare Advantage plan and return to Original Medicare during AEP, you do not automatically get guaranteed issue rights for a Medigap plan. In most states, you will face medical underwriting, which means you could be denied coverage or charged higher premiums based on your health. This is one of the most consequential and least understood AEP decisions.