7. How do I enroll in Medicare? Posted on September 11, 2017 at 12:21 pm.Written by advantage_admin To enroll in Part A, you should do it during: The initial enrollment period – When you become eligible for Medicare for the first time (three months before your birthday, on the month of your birthday, and for three months after your birthday). The General Enrollment Period – Every year, from January 1 to March 31; coverage begins on July 1. A Special Enrollment Period – This period happens at any given time of the year and for various reasons. Medicare will determine when a special enrollment period begins. To enroll in Part B in Puerto Rico: To enroll in Part B, members must fill out the Application for Enrollment in Medicare Part B (CMS-40B). This form and its instructions are available in both English and Spanish at Medicare.gov. Please contact Social Security if you do not have Medicare and you wish to enroll in Part A first. Some people may have to pay a premium for Part A. Post navigation 2. Which Advantage plan should I choose?8. What do PPO, HMO, POS, and SNP mean?