You can be eligible for Medicare coverage if you fall into one of three categories. First, you are eligible if you or your spouse worked for at least 10 
years in Medicare-covered employment and you are at least 65 years old and a citizen or permanent resident of the United States. Second, you can qualify if you are a younger person with a disability, or you suffer from end stage renal disease. Third, if you are at least 65 years old and are already receiving retirement benefits from Social Security or the Railroad Retirement Board, or if you could receive them, then you are eligible to receive Part A benefits without having to pay premiums.
You can enroll in Medicare in one of two ways: either you are enrolled automatically, or you can be accepted through application to the program. You will be enrolled automatically in the Medicare program if you are already getting Social Security or Railroad Retirement benefits when you turn 65. In that situation, you are enrolled automatically in both Part A and Part B, and your Medicare card will be mailed to you about three months before your 65th birthday. In addition, if you are disabled, you should get your Medicare card in the mail automatically after you have been receiving Social Security or Railroad Retirement Board disability benefits for 24 months.
If you are not automatically enrolled in the Medicare program, you must apply for benefits. You can apply by calling the Social Security Administration office closest to you, or by calling 1 (800) 772-1213. You should apply three months before you turn 65 to avoid a possible delay in coverage. Your seven-month initial enrollment period begins at that time. If you do not apply for Medicare within the seven-month period, you will have to wait until the next general enrollment period. General enrollment periods are held from January 1 to March 31 of each year. Coverage then begins on July 1st. Additionally, if you do not apply during your initial enrollment period you may be charged a penalty of approximately 10% on your monthly premium for each year you were qualified to enroll but did not.
You may also be eligible for a Special Enrollment Period if you or your spouse were covered by a creditable group plan through your employer or a union when you first became eligible for Part B coverage.
If you are not automatically enrolled in Medicare, you should apply as soon as possible. Delays in your coverage are much more likely to occur the longer you wait. If you have any questions about how to apply, you can contact the Social Security Administration office in your area or call the toll-free number, 1 (800) 772-1213.
For more information, see: Centers for Medicare & Medicaid Services, U.S. Department of Health and Human Services, Medicare & You (2015), available at http://www.medicare.gov/Pubs/pdf/10050.pdf and for alternative formats visit http://www.medicare.gov/Publications/Search/results.asp?PubID=10050&Publanguage=1&Type=PubId (last visited May 28, 2015); Centers for Medicare & Medicaid Services, Medicare: The Official U.S. Government Site for People with Medicare, http://www.medicare.gov (last visited May 28, 2015).