Most people know that the Medicare Annual Enrollment Period is October 15 through December 7. The barrage of commercials featuring aged sports icons and actors not seen on television in decades starts in early October and doesn’t end until well after the holidays. But there is another enrollment period called the Open Enrollment Period (OEP) from January 1 through March 31 in which you can still change your Advantage Plan if you are not happy with your previous choice. This coincidentally coincides with the Medicare General Open Enrollment Period in which you can sign up for Medicare if you failed to do so during your Initial Enrollment Period (when you turn 65). During this OEP period, you can change to a different Medicare Advantage Plan or switch to Original Medicare (and enroll in a Part D drug plan). If you want to add a Medicare Supplemental Plan, you might have to go through underwriting (answer medical questions) unless you were in your Advantage Plan for less than a year or have a Special Enrollment Period that applies (such as having moved out of the service area of your Advantage Plan).Reasons you might not be happy with your original choice include: Discovering your doctor or doctors are not in network for the plan – Finding that some of your medications are not in the formulary of the plan – Discovering the cost of your medications on the plan are higher than expected – Finding the network of available doctors and specialists too limitedWhatever the reason, you will be able to change your plan and not have to wait until October 15 when the Annual Enrollment Period begins again. If you make a plan selection in January, your new plan will start February 1. If you wait until March, your effective date would be April 1. Unlike the Annual Enrollment Period in which you can make several choices with your last application submitted being the plan you end up with, you will have only one opportunity to choose a plan during OEP.