2. How do I enroll in Medicare Part B? Posted on September 11, 2017 at 12:01 pm.Written by advantage_admin All citizens who are eligible for Medicare Part A will also be eligible for Part B. Part B is optional, since it has a monthly fee, and additional charges and/or fines could apply if the member does not enroll within a specified time period. Those who fail to enroll in Medicare Part B when they become eligible for the first time and are not eligible for a Special Enrollment Period could face late enrollment penalties. This could entail an increase in the monthly premium of 10% for each 12-month period during which you were eligible for Part B but did not enroll. You would have to pay this higher premium as long as you have Medicare Part B. To enroll in Part B: Send an online application to Social Security. If you already started filling out your online application and have a re-entry number, you may log in again to complete your application. Visit your local Social Security Office. Call Social Security at 1-800-772-1213 (TTY: 1-800-325-0778). If you are or were a railroad worker, please contact the Railroad Retirement Board (RRB) at 1-877-772-5772. Complete your Part B enrollment application (CMS-40B). The form and instructions are available in English. And please remember that you must have Part A to be able to apply for Part B. The amount payable for Part B will be calculated based on the member’s reported income tax. Post navigation 1. What is Medicare Part B?3. What does Medicare Part B cover?