ACA Marketplace open enrollment: when it opens
In short
In most states, ACA Marketplace open enrollment runs November 1, 2026 through January 15, 2027. Enrolling by December 15 starts coverage January 1; enrolling after that starts coverage February 1. A handful of states run their own state-based marketplace with different dates.
Two deadlines matter here, not one: when the window closes, and the earlier date inside it that decides whether coverage starts January 1 or a month later.
The federal window
For the roughly two-thirds of states using HealthCare.gov, open enrollment runs November 1, 2026 through January 15, 2027. Enroll by December 15 and coverage begins January 1, 2027. Enroll between December 16 and January 15 and coverage begins February 1, 2027 instead.
States that run it differently
State-based marketplaces set their own calendars, and several extend past January 15 — some into late January or beyond. Anyone in a state-run exchange should check that state’s marketplace directly rather than assuming the federal dates apply; using the wrong deadline is the most common way people miss enrollment entirely.
Why the December 15 split exists
Insurers need lead time to activate a plan starting January 1. Enrollments after December 15 still count for the year, but processing pushes the effective date to February 1 — leaving a gap month uninsured unless other coverage bridges it.
Outside the window
A Special Enrollment Period opens for 60 days after a qualifying life event: losing job-based coverage, aging off a parent’s plan, moving to a new area with different plan options, marriage, or the birth or adoption of a child. It works independently of where the calendar sits relative to November 1 or January 15.
Common questions
Does the window apply everywhere?
The federal HealthCare.gov window (November 1 to January 15) applies to states that use the federal marketplace. States that run their own exchange — including California, New York, and several others — set their own dates, often extending into late January.
What is the actual difference between enrolling by December 15 versus later?
It only changes the start date of coverage, not eligibility or the plan available. Enroll by December 15 and coverage starts January 1. Enroll between December 16 and January 15 and coverage starts February 1 instead — a full month later.
Can I enroll outside this window at all?
Only with a qualifying life event — losing other coverage, moving, marriage, or having a baby — which opens a 60-day Special Enrollment Period regardless of the calendar.
Does this overlap with Medicare's enrollment window?
Yes, October 15 through December 7 for Medicare overlaps most of this window, but they serve different populations and neither substitutes for the other — someone aging into Medicare mid-window needs to handle both separately.
Source: HealthCare.gov, Centers for Medicare & Medicaid Services · retrieved September 12, 2026