Anyone is able to enroll in a Marketplace during the Open Enrollment Period between November 1 and January 15 (these dates vary a bit by state). Starting in 2026, the Open Enrollment Period will be between November 1 and December 15.
Coverage purchased prior to December 15 will start on January 1. Coverage purchased after December 15 will start on February 1.
Outside of the Open Enrollment Period, you will require a Special Election Period (SEP) to be considered eligible for enrollment in a Marketplace plan.
Typical SEPs include loss of other coverage, moving, or having a baby, though others do exist.