If you are not yet eligible for Medicare, your time frame for enrolling in Part D is the same as for Part B — a seven-month period that includes your birth month, plus the three months immediately before and after your birth month. Your benefit begins on your 65th birthday or the first day of the month following enrollment, whichever comes later. You may be subject to a penalty premium if you do not enroll in Part D during this initial enrollment period.
If you currently have Medicare, you may enroll in a prescription drug plan from October 15, 2018 until December 7, 2018. If you did not enroll when you were first eligible for the benefit, you may be subject to a penalty premium. Low-income beneficiaries who are eligible for Extra Help will not face this penalty. Drug coverage will begin on January 1, 2019. CMS encourages beneficiaries to enroll early to reduce the chance of problems with drug coverage beginning in January. If you are currently in a stand-alone drug plan or a managed care plan, you can enroll, switch plans or disenroll once a year during the Annual Coordinated Election Period (ACEP). In 2018 the ACEP will run from October 15 to December 7.

If you are in a private Medicare Advantage managed care plan, you may switch to coverage under Original Medicare during the Medicare Advantage Annual Disenrollment Period from January 1 to February 14 in 2019. You also have the option of joining a Part D stand-alone plan at this time, but are not required to do so. You may not switch to another managed care plan during this period, however.