Open enrollment for 2026 ACA marketplace coverage has already closed, but it's worth understanding the calendar now, both to see how it played out and to know what's coming for 2027 coverage. The 2026 Open Enrollment Period ran from November 1, 2025 through January 15, 2026 for the 30 states using the federal HealthCare.gov exchange. * Eight states plus D.C. — California, Connecticut, D.C., Illinois, New Jersey, New York, Pennsylvania, and Rhode Island — ran their own state-based exchanges with a later cutoff, January 31, 2026, giving residents there roughly two extra weeks to enroll or make changes. * Timing your sign-up mattered for when coverage actually started. On HealthCare.gov, enrolling by December 15, 2025 meant coverage began January 1, 2026. Sign up after that date but before the window closed, and coverage instead started February 1, 2026 — a full month later. * Looking ahead, most states are scheduled to open enrollment for 2027 coverage on November 1, 2026, running through December 15, 2026 — a shorter window than 2026 had. That said, the rule shortening the enrollment period was vacated by a federal judge in June 2026, so it's genuinely unclear whether the 2027 window will end up shorter than usual or revert to the longer January 15 deadline most states have used in recent years. * Outside of open enrollment, you can only sign up for marketplace coverage through a Special Enrollment Period triggered by a qualifying life event — losing job-based coverage, moving, marriage, or having a baby, among others.