Your Medicare Part D Initial Enrollment Period (IEP) is a seven (7) month window of time that starts three months before your Medicare eligibility month (or 65th birthday month), plus the month of your Medicare-eligibility month (65th birthday month), and continues for three months after your birthday or Medicare eligibility month.

For example, if you turn 65 on February 10th, your birthday month is February, and your "Initial Enrollment Period" starts on November 1st (3 months before your birthday month) and continues through May 31st (3 months after your birthday month).  Your Medicare Part D IEP therefore is November 1st through May 31st.

You can use this same 7-month Initial Enrollment Period window to enroll in a Medicare Part D prescription drug plan (PDP) or a Medicare Advantage plan with drug coverage (MAPD).  If you have some other form of drug coverage (such as VA coverage) and you do not want Part D prescription coverage, you can join a Medicare Advantage plan without drug coverage (MA).


Question: When does my Medicare Part D drug coverage begin?

Your Medicare Part D plan begins (or becomes effective) either

(1) the first day of the month of eligibility if you enroll into a Medicare plan before your birthday (or eligibility) month or
(2) the first day of the month following the enrollment month if you enroll into a Medicare plan during or after your birthday (or eligibility) month.

Continuing the example of a February 10th 65th birthday
If you turn 65 in February, your "Initial Enrollment Period" (IEP) runs from November through May - however, your Medicare plan coverage cannot start any sooner than the first day of your birthday month (or February).  After your eligibility month, coverage will begin the 1st day of the month after enrollment.  So if you enroll in a Medicare Part D plan in February, your coverage will begin on the first day of the month following your enrollment or March 1st.

Exception to the "birthday rule" --- If your birthday is on the first of the month (for example, February 1st), then your coverage would start the first day of the month before your birthday (January 1st).

Question:  I have several health issues and use a number of prescriptions on a regular basis, when should I join a Medicare Part D drug plan?

Consider enrollment before your Medicare eligibility month.
In our example of a "February 10th birthday", this would mean enrolling into a Medicare Part D plan before February 1st.  And if your health is changing, you may wish to enroll in a Medicare plan closer to your Medicare eligibility date so that you are able to choose the Medicare plan that most economically meets your health and prescription needs.  For example, consider enrollment in mid-January for a February 1st start or effective date.

Important: If you want to have Medicare coverage starting on the first day of your birthday month (February), you should sign up for Medicare no later than the end of January.


Question:  I do not use any medications and have no health issues, when should I join a Medicare plan?

Anytime during your IEP -- enrollment depends on your personal preference (or risk tolerance).
If you have no health concerns, you can enroll into a Medicare drug plan earlier in your 7-month AEP for a February 1st effective date, thereby ensuring drug coverage at the beginning of your Medicare eligibility --- or you can wait and enroll later (such as at the end of the IEP) if you do not anticipate needing the Medicare plan coverage - and wish to save on Medicare plan premiums.


Question:  What happens if I miss my IEP and don't join a Part D drug plan when I am first eligible?

If you miss your Medicare Part D Initial Enrollment Period, and then later join a Medicare Part D plan, you may be subject to a permanent late-enrollment premium penalty (LEP) that you will pay in addition to your monthly premium as long as you have a Part D plan. 

Please read our FAQ: "I did not enroll in a Medicare Part D plan when I was first eligible, how will I calculate my Medicare Part D late-enrollment premium penalty?"

Question:  What if I enroll into a Medicare plan early and then change my mind as I get closer to my Medicare eligibility month?  Am I allowed to choose another Medicare plan during the IEP?

Not usually.  In general, once you choose a Medicare Part D or Medicare Advantage plan during your IEP, then you will not be given an opportunity to choose another plan, even if your health or medication needs change.  Medicare notes in the Medicare Part D enrollment manual that

"[o]nce an individual uses his/her IEP for Part D enrollment and this enrollment becomes effective, this enrollment period [IEP] ends."

And, as already noted above, the effective date for Medicare Part D enrollment during the IEP are based on the following rules:

"Enrollment requests made prior to the month of eligibility are effective the first day of the month of eligibility.  Enrollment requests made during or after the first month of eligibility are effective the 1st of the month following the month the request was made."

However, the Medicare Part D enrollment manuals also take into consideration Multiple enrollment transactions and notes that:

"[m]ultiple transactions occur when CMS receives more than one enrollment (or disenrollment) request for the same individual with the same effective date in the same reporting period.  . . . [and] [g]enerally, the last enrollment request the beneficiary makes during an enrollment period will be accepted as the PDP into which the individual intends to enroll. If an individual requests enrollment in more than one PDP for the same effective date and with the same application date, the first transaction successfully processed by CMS will take effect."

As clarification, the Medicare manuals provide the following example of multiple enrollments:

"Two PDP sponsors receive enrollment requests from one individual. PDP #1 receives a form on December 4th and PDP #2 receives a form on December 10. Both organizations submit enrollment transactions, including the applicable effective date and application date. The enrollment in PDP #2 will be the transaction that is accepted and will be effective on January 1 because the application date on the enrollment transaction is the later of the two transactions submitted."

Source:
Medicare Prescription Drug Benefit Manual, Chapter 3 - Eligibility, Enrollment and Disenrollment (updated August 12, 2020)