You can enroll in Medicare Part D, which is prescription drug coverage, during several periods:

1. Initial Enrollment Period (IEP): This starts three months before you turn 65, includes your birthday month, and ends three months after. If you’re under 65 and qualify for Medicare due to disability, your IEP starts 24 months after you begin receiving disability benefits.
2. General Enrollment Period (GEP): If you missed your Initial Enrollment Period, you can enroll during the General Enrollment Period from January 1 to March 31 each year. Coverage begins on July 1.
3. Annual Enrollment Period (AEP): This runs from October 15 to December 7 each year. During this time, you can join, switch, or drop a Part D plan, with coverage starting on January 1 of the following year.
4. Open Enrollment Period for Medicare Advantage (OEP): If you’re enrolled in a Medicare Advantage plan, you can make changes to your Part D coverage between January 1 and March 31.
5. Special Enrollment Periods (SEPs): These are available in certain situations, such as if you lose other credible prescription drug coverage, move out of your plan’s service area, or experience other qualifying life events.  Typical situations are when a person exits an employer health insurance plan, of if a person currently has Part D drug coverage and they move to a different County or State.

It’s important to sign up for Part D when you’re first eligible to avoid late enrollment penalties, unless you have other credible prescription drug coverage.