Enrollment in Original Medicare (which includes Medicare Part A and Part B) may or may not be automatic — it depends on your situation.
If you already receive Social Security or Railroad Retirement Board benefits or become eligible early due to disability, you’re automatically enrolled. Otherwise, you’ll need to enroll yourself during your Initial Enrollment Period (IEP).
You can join either Part A or Part B. You are not required to enroll in Part B immediately since you will be charged a premium. Keep in mind that if you postpone enrolling in Part B, you will incur a late enrollment penalty and your coverage will be more expensive. Learn how to avoid a Medicare Part B late enrollment penalty.
You can enroll in Original Medicare online at the Social Security website or by calling or visiting your local Social Security office.
You must have both Part A and Part B in order to enroll in a Medicare Advantage (Part C) or a Medicare Supplement plan. You just need Part A or Part B for a Medicare prescription drug (Part D) coverage.