Fall Open Enrollment occurs from October 15 to December 7 of every year. Learn more about Fall Open Enrollment choices

You are limited in when you can change your Medicare healthplan during the year.

1. You can switch Medicare private plans during Fall Open Enrollment (Fall Open Enrollment is sometimes referred to as the Annual Coordinated Election Period – ACEP) which runs from October 15 through December 7 in 2012. Your new coverage starts January 1. During this period you can change your choice of health coverage, and add, drop or change Medicare drug coverage. (You can make as many changes as you need during this period, but only your last coverage choice will take effect January 1. However, to avoid enrollment problems, it is best to make as few changes as possible).
   Note: If you are changing plans to join a Medicare Medical Savings Accounts (MSA), you can usually only do so during the Fall Open Enrollment Period.  
2. You can switch from your Medicare private health plan (except MSA plan) to Original Medicare during the Medicare Advantage Disenrollment Period (MADP).You can only make this coverage change if you have a Medicare private health plan (also known as a Medicare Advantage plan). The MADP will occur every year starting in 2011, from January 1 to February 14.
   If you have a Medicare private health plan you will be able to switch to Original Medicare with or without a stand-alone prescription drug plan. Changes made during this period will become effective the first of the following month. For example, if you switched from a Medicare Advantage plan to Original Medicare and a stand-alone prescription drug plan in February, your new coverage would begin March 1.
   (More Info HERE)