The Initial Enrollment Period (IEP) for Parts A and B is 7 months, starting 3 months before the month of your Medicare eligibility and ending 3 months after the month of eligibility. The month of eligibility is the month of your 65th birthday, if you become eligible for Medicare because you are turning 65 years old. Or, if you become eligible due to a disability, your month of eligibility is the 25th month of receiving Social Security Disability Insurance (SSDI)

Note: If you delay your enrollment into Part B, you may have to pay a late enrollment penalty of 10% of the current Part B premium amount for each 12-month period you delayed enrollment. However, if you have coverage from an employer group health plan based on current employment, you may not have to pay the penalty.

 If you are 65 years old or older and owe the penalty, you have to pay the penalty for as long as you are enrolled in Part B. If you are younger than 65, have Medicare because of a disability and owe the penalty, the Part B penalty will end when you turn 65 and qualify for Medicare based on age.

Initial Coverage Election Period for Part C 

Enrolling in Medicare Part C or a Medicare Advantage (MA) plan is optional. If you want to enroll in a Medicare Advantage plan you must be entitled to both Parts A and B. Your Initial Coverage Election Period (ICEP) to join an MA plan may be 3 months or 7 months as illustrated by the examples below.

Example 1: A person’s 65th birthday month is April. His IEP for Part B is January 1 to July 31. He enrolls in Part B and the effective date of his Part A and Part B benefits is April 1. Because he enrolls in Medicare during his IEP, his ICEP to join MA plans is January 1 to July 31, the same 7 months as his IEP for Part B.
Example 2: A person’s 65th birthday month is April and her IEP for Parts A and B is January 1 to July 31. She does not enroll in Part B because she continues to work and is covered by her employer’s group health plan. She retires and then enrolls in Part B which becomes effective December 1. In this case, her ICEP to enroll in an MA plan is September 1 to November 30, 3 months before the effective date for both Parts A and B.
Initial Enrollment Period for Part D
If you are newly eligible for Medicare, your IEP to enroll in a Part D plan is the same as your IEP for Parts A and B. To enroll in a Medicare Part D plan, you must be eligible for either Part A or Part B. People who have Medicare due to a disability have another IEP for Part D when they turn 65 years old. If you don't enroll in a Medicare drug plan during your IEP, you can enroll during the Annual Election Period (October 15 – December 7) or during a Special Enrollment Period, explained below. Also, if you do not join a Part D plan during your IEP, do not have creditable coverage for your drugs (prescription drug coverage that is at least as good as Medicare’s Part D benefit), and you
enroll later, you may incur a penalty. The penalty is 1% of the average national premium for every month you were eligible and did not sign up. (The average national premium is $32.34 in 2011 and changes each year.) This amount is added to your drug plan premium and you pay it as long as you are in a Part D plan or MA plan with prescription drug coverage. Note: If you enroll in an MA plan during the ICEP or Part D plan during the IEP and the plan becomes effective, you may not make another election even though the ICEP or IEP has not expired.
General Enrollment Period
People who did not enroll in Part A or B during their IEP, or terminated their Part A or Part B benefits and want to re-enroll, may enroll in
either or both Parts during the General Enrollment Period (GEP), which is January 1 to March 31 of each year. If you enroll during the GEP, your benefits will begin the following July 1. If you enroll in Part B during the GEP, you may have to pay the Part B late enrollment penalty mentioned above.
Annual Election Period
The Annual Election Period (AEP) is October 15 to December 7 of every year beginning in 2011. During this time frame, people can join, change or drop an MA plan or Part D plan. For example:
• If you did not enroll in an MA plan during your ICEP or a Part D plan during your IEP, you may enroll in an MA plan or Part D plan during the AEP.
• If you are already in an MA plan or Part D plan, you may change plans or disenroll from your plan during the AEP.
• If you had an MA plan and went back to Original Medicare and now want to be in an MA plan again, you may enroll during the AEP.
You may make more than one election during the AEP. Your final election during that period is the one that counts. The last election (or only election) made during the AEP will be effective January 1 of the following year.
Special Enrollment Period
A Special Enrollment Period (SEP) exists for Part B, and Special Election Periods (also referred to as SEPs) exist for MA plans and Part D plans in certain circumstances (see below). For Part B, an SEP is available only for people who delay enrollment in Part B because they
have employer group coverage. If you become eligible for Medicare at 65, and have coverage from an employer group health plan based on your or your spouse’s employment, you may delay enrollment in Part B. When you stop working or your employer group health coverage ends, you have an SEP to enroll in Part B. The SEP is 8 months following the end of employment or employer group health coverage, whichever is earlier. If you enroll during the SEP, you do not owe the late enrollment penalty for Part B (explained above). Note: if you have end stage renal disease, you do not have this same SEP. 
Special Election Periods
Special Election Periods (SEPs) for MA and Part D plans may be available depending on the situation. Examples:
• If you move, you may change to a different plan not offered in the area where you formerly lived.
• If your coverage through your employer or union group health plan ends, you have an SEP to enroll in an MA or Part D plan. The SEP
ends 2 months after the month your coverage through the group plan ends.
• If you are eligible for full Medi-Cal benefits, you have an ongoing SEP to enroll in or change MA or Part D plans.
• If you lose your full Medi-Cal benefits, you have a 3-month SEP to change MA or Part D plans, starting the month you are notified of
the loss of Medi-Cal eligibility.
• If you become eligible for the low-income subsidy (LIS) or extra help, you have an ongoing SEP as long as you qualify for the
LIS. You can change Part D plans or MA plans with prescription drug coverage on a monthly basis.
• If you lose the LIS, you have a 3-month SEP beginning in the month you receive notice of losing the low-income subsidy.
• If you enroll in Part B during the GEP (but are not entitled to premium-free Part A), you have an SEP to enroll in a Part D plan between
April 1 and June 30. If you enroll in a Part D plan during this SEP, your plan becomes effective July 1.
• If you enroll in an MA plan during the ICEP around your 65th birthday, you have an SEP to disenroll from the MA plan during your first
12 months in the plan and return to Original Medicare.

Medicare Advantage Disenrollment Period
Beginning in 2011, the Medicare Advantage Disenrollment Period (MADP) runs between January 1 and February 14 of each year and
allows beneficiaries to disenroll from their MA plan and return to Original Medicare. You cannot switch from one MA plan to another or enroll in an MA plan during the MADP. If you disenroll from an MA plan, you have a coordinating SEP to enroll in a stand-alone PartD prescription drug plan. The SEP ends February 14 or when you enroll in a stand-alone Part D plan, whichever is sooner.