A special enrollment period (SEP) is a time outside of open enrollment* during which you can purchase a new health insurance policy. *Open enrollment for health insurance is a time each year when anyone can purchase or change a health insurance policy for any reason. For 2017 plans, open enrollment was November 1, 2016 – January 31, 2017. 2018 open enrollment will run from November 1, 2017 – December 15,