The Medicare Advantage Open Enrollment Period: What You Can Change January Through March

Most people learn about the Annual Enrollment Period, the main window from October 15 to December 7 when Medicare plan changes take effect January 1. Far fewer know that a second, more limited enrollment window opens every January 1 and runs through March 31. This Medicare Advantage Open Enrollment Period, or OEP, gives people already in Medicare Advantage one more chance to make a change during the year, with important restrictions on what you can and cannot do during it.

Bryce's Take

The OEP is the call I get in January and February from people who enrolled in an Advantage plan in October and then discovered their cardiologist is not in network, or their drug is on Tier 4, or the prior auth for a procedure they need is being denied. The window to make a change is real and it is open until March 31. What I always tell them: if you want to switch back to Medigap and your health has changed since you first enrolled, we need to move quickly and carefully because underwriting may apply.

What the OEP allows

During the Medicare Advantage Open Enrollment Period, you can make one plan change if you are already enrolled in a Medicare Advantage plan. Specifically, you can switch from one Medicare Advantage plan to a different Medicare Advantage plan, or you can disenroll from Medicare Advantage entirely and return to Original Medicare (with the option to enroll in a standalone Part D plan). The change takes effect the first day of the month following your enrollment request. A request made in January takes effect February 1; one made in March takes effect April 1.

What the OEP does not allow

The OEP has important restrictions. You cannot use the OEP to switch from Original Medicare to Medicare Advantage, that change is only possible during AEP (October 15 to December 7) or through a qualifying Special Enrollment Period. You can only make one plan change during the OEP, not multiple changes. And if you switch from Advantage back to Original Medicare during the OEP, enrolling in a Medigap plan at that point requires medical underwriting in most states because the OEP does not trigger a guaranteed issue right for Medigap.

How it differs from AEP

The Annual Enrollment Period, which runs October 15 to December 7, is open to all Medicare beneficiaries and allows switching in any direction, Original Medicare to Advantage, Advantage to Advantage, Advantage to Original Medicare, or changing Part D plans. Changes made during AEP take effect January 1. The OEP is more limited: it only applies to current Advantage enrollees, allows one change, and does not allow switching from Original Medicare to Advantage.

Common reasons to use the OEP

Beneficiaries use the OEP most often when they enrolled in an Advantage plan during AEP and then quickly discovered a problem, their physician is not in network, their medication is on a high cost-sharing tier, or the prior authorization burden is significant. The OEP provides an escape valve for people who made a plan choice in the fall that turned out to be wrong in practice. It is also used by people who received unexpected medical diagnoses in January or February and realize their current Advantage plan is not suited to new care needs.

The Medigap complication if you disenroll from Advantage

If you use the OEP to disenroll from Advantage and return to Original Medicare, you may want to add a Medigap plan. However, the OEP does not come with a guaranteed issue right for Medigap in most states. That means you would need to pass medical underwriting to purchase Medigap, and if your health has changed, you may be declined or charged more. The exception is if you are in your first year of Advantage enrollment, you have a one-time trial right to return to Medigap without underwriting in that first 12 months. Outside the first year, Medigap access depends on your health and state protections.

The 5-star plan exception

There is one more enrollment window worth knowing about alongside the OEP: the 5-star Special Enrollment Period. If a Medicare Advantage or Part D plan in your area earned 5 stars from CMS, you can switch to that plan once during the period December 8 through November 30 of the following year. This window overlaps with but is separate from the OEP and is available regardless of whether you are already in Advantage or in Original Medicare.

Bryce Casson

Licensed Independent Medicare Broker

Bryce Casson is an independent Medicare insurance broker who works with every major carrier. He does not represent any single insurer, which means his recommendations are based on what actually fits each client's situation, not on commissions or quotas.