Open enrollment starts every year on October 15, and it runs through December 7. Any plan changes you make will not take effect until January 1. During open enrollment, you are allowed to switch from traditional Medicare to a Medicare Advantage Plan, or from Medicare Advantage back to traditional Medicare. You’re also allowed to exchange one Medicare Advantage Plan for another. Open enrollment is also important for prescription drug coverage. During this period, you are allowed to switch from one Part D plan to another. It’s important to consider your options because different plans can have entirely different coverage, and you total costs can vary greatly.