Medicare is the Federal health insurance program for Americans age 65 and older and for certain disabled Americans. If you are eligible for Social Security or Railroad Retirement benefits and are age 65, you automatically qualify for Medicare.

Medicare Enrollment Options1
Enrollment Period
When It Occurs
Who Needs It 
Initial enrollment period This period spans seven months—starting three months before your 65th birthday month and ending three months after your birthday month.  Those enrolling in Medicare Part A (hospital insurance), Part B (medical insurance) and Part D (prescription-drug plan). Also applies to those who choose to receive their benefits through Medicare Advantage plans, also known as Part C.  Those receiving Social Security are automatically enrolled in Parts A and B unless coverage is declined. If you don't have coverage from an employer plan, you'll pay an ongoing late enrollment penalty of 10% of the Part B premium for every 12 months you delay signing up. 
Special enrollment periods Within eight months after you stop working.  Those about to lose employer coverage and have delayed enrolling in Part B.  Separate special enrollment periods also exist for Medicare Advantage and Part D plans. 
General enrollment period Jan. 1 - Mar. 31 Those who do not enroll in Parts A and B during their initial enrollment period or special enrollment period.  Coverage doesn't become effective until July 1. 
Annual election period Nov. 15 - Dec. 31  If you don't enroll in a Medicare plan with drug coverage during your initial enrollment period, you can do so now. If you did, you can change or drop these plans now.  You have to enroll in Medicare Parts A and B first. 
Medicare Advantage open enrollment period Jan. 1 to March 31  Those who want to join, drop or change a Medicare Advantage plan.  Beneficiaries with prescription drug coverage can't drop it at this time; those without drug coverage can't add it. 

Source:  Anne Tergesen, Retirees Snared by Medicare, The Wall Street Journal, December 30, 2009

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