OEP stands for Open Enrollment Period, and in the context of Medicare, there are actually two distinct windows that go by this name. The one most people mean is the Annual Open Enrollment Period, which runs from October 15 through December 7 each year. There’s also a separate Medicare Advantage Open Enrollment Period from January 1 through March 31. Both give you a chance to change your Medicare coverage, but the rules for each are different, and several new policies took effect for 2025.
The Two Medicare Open Enrollment Periods
The Annual Open Enrollment Period (October 15 to December 7) is the broadest window for making changes. During this time, you can join, drop, or switch a Medicare Advantage plan with or without drug coverage. You can also join, drop, or switch a standalone Medicare Part D drug plan if you’re in Original Medicare. And you can change how you get coverage entirely, switching from Original Medicare to a Medicare Advantage plan or the other way around.
The Medicare Advantage Open Enrollment Period (January 1 to March 31) is more limited. It’s only available to people who are already enrolled in a Medicare Advantage plan. During this window, you can switch to a different Medicare Advantage plan or drop your Medicare Advantage plan and return to Original Medicare. If you return to Original Medicare, you can also join a separate Medicare drug plan. You cannot use this period to go from Original Medicare into a Medicare Advantage plan for the first time.
What’s New for 2025
The Centers for Medicare and Medicaid Services finalized a set of rule changes that affect how plans are sold, how agents are paid, and how your personal information is handled. These changes took effect for coverage beginning in 2025.
One significant update involves agent and broker compensation. CMS redefined “compensation” to set a clear, fixed amount that agents and brokers receive regardless of which plan they enroll you in. The goal is to reduce the incentive for agents to steer you toward plans that pay them higher commissions rather than plans that best fit your needs.
There are also new protections around your personal data. Any personal information collected by a third-party marketing organization (the companies that run Medicare plan comparison websites, call centers, and mailers) can now only be shared with another marketing organization if you give prior express written consent. Previously, your information could be passed between these organizations more freely, often resulting in a flood of unwanted calls and mailers.
Changes for People With Both Medicare and Medicaid
If you qualify for both Medicare and Medicaid (known as being “dually eligible”), several new rules apply specifically to you. The quarterly special enrollment period for Part D drug plans has been replaced with a monthly special enrollment period. This means you can switch your standalone prescription drug plan once per month instead of once per quarter, giving you more flexibility to find a plan that covers your medications at the lowest cost.
CMS also created a new “integrated care” special enrollment period. This allows dually eligible individuals to enroll in an integrated dual eligible special needs plan (D-SNP) when they’re also receiving Medicaid services through an affiliated managed care plan. The idea is to make it easier to coordinate your Medicare and Medicaid benefits under one roof rather than dealing with separate plans that don’t communicate with each other.
Starting in 2026, out-of-network cost sharing for D-SNP preferred provider organization plans will be capped for specific services. And the threshold for what CMS calls “D-SNP look-alikes,” regular Medicare Advantage plans that enroll a high percentage of dually eligible members without offering the coordination benefits of a true D-SNP, dropped from 80% to 70% in 2025 and will drop further to 60% in 2026. This pushes more plans serving low-income enrollees to meet the stricter standards of genuine special needs plans.
When Your New Coverage Starts
The effective date of your new plan depends on which enrollment period you use. Changes made during the Annual Open Enrollment Period (October 15 to December 7) take effect on January 1 of the following year. Changes made during the Medicare Advantage Open Enrollment Period (January 1 to March 31) generally take effect the first of the month after the plan receives your enrollment request.
If you make multiple changes during either window, only your last choice counts. So if you switch to Plan A in October and then switch again to Plan B in November, you’ll be enrolled in Plan B on January 1.
OEP Outside of Medicare
Worth noting: “OEP” doesn’t always refer to Medicare. In workplace benefits, open enrollment is the annual window your employer gives you to change health insurance, dental, vision, and other benefits. The Affordable Care Act marketplace also has its own Open Enrollment Period, typically running from November 1 through January 15, though some states extend this deadline.
In health and fitness contexts, OEP sometimes refers to the Otago Exercise Program, an evidence-based fall prevention program for older adults. It involves individually prescribed strength and balance exercises delivered in person or online, with monthly check-in calls during a self-management phase. The National Council on Aging lists it as an evidence-based program, and updated guidance was released in 2023. But if you arrived here searching for Medicare information, this is a different OEP entirely.