If you enroll by midnight on Dec. 15 (5 a.m. Eastern time on Dec. 16), your coverage starts Jan. 1 in states that use the federally run HealthCare.gov. The overall sign-up deadline is typically Jan. 15. But because a federal holiday — Martin Luther King Jr. Day — falls on that date in 2024, it’s been extended to midnight on Jan. 16 (5 a.m. Eastern time on Jan. 17).
If you enroll after Dec. 15 but before the deadline in January, your coverage starts Feb. 1.