Just a few comments on the information here: You can actually enroll in Part D if you have only Part A. If you are on an employer plan, it Is important to determine if your employer plan is creditable or non-creditable for Part D. This indicates whether the employer plan expected to pay as much or more as a Part D plan. If it is non-creditable, then you will still be subject to the Part D late enrollment penalty when you do enroll in Part D. (This detail does not apply for Part B.)