Annual enrollment is from October 15th to December 7th. During this period, one can change insurance companies as many times as they wish. The company one has as of December 8th, this is the plan that will go into effect on January 1st. Open Enrollment starts from January 1st to March 31st, a person can make one change to another insurance company. This will be the company the person will be with for the remaining of the year.
