November 1, 2017 - Open enrollment starts. You can enroll, renew, or make changes to a 2017 insurance plan through the ACA Marketplace in your state, or private insurance website.
December 15, 2017 - Last day of open enrollment for coverage to start January 1, 2017. Must pay new health insurance on or before this date
January 31, 2018 - Last day of open enrollment at all. After this date, to enroll or change plans through the marketplace only if you qualify for a Special Enrollment Period.