It is very important to purchase your Supplement Plan within the Open Enrollment Period because during this time, you will not be required to do medical underwriting (answer health questions) in order to qualify for the Plan. After this window of time, if you want to apply for a Supplement Plan, you can still do so. However, you will have to answer several health questions, pass medical underwriting, and the carrier can choose not to accept your enrollment. Therefore, it is important to know these dates, and not miss this important window of time.