Open Enrollment runs November 1 through December 15, and during this window, anyone can shop for an individual health insurance plan, with coverage starting January 1.
Outside of that window, you'll need a Qualifying Life Event (QLE) to enroll in or change an individual health insurance plan — unless your state runs an extended Open Enrollment period. You can check to see if your state' has an extended open enrollment here: Need health insurance? | HealthCare.gov
Qualified Life Events:
Loss of qualifying health coverage
Losing job-based coverage (including through a spouse or parent)
Aging off a parent's plan at 26
Losing Medicaid or CHIP eligibility
Losing individual/marketplace coverage for a reason other than not paying premiums
COBRA coverage ending
Household changes
Getting married
Divorce or legal separation (in states where it affects coverage eligibility)
Having a baby, adopting a child, or placing a child for foster care
Death of someone on the policy
Residence changes
Moving to a new ZIP code or county where different plans are available
A student moving to or from school
A seasonal worker moving to or from where they live and work
Moving to or from a shelter or transitional housing
ICHRA and QSEHRA specific
Becoming newly eligible for an ICHRA or QSEHRA — this is itself a QLE. Employees (and their dependents) get a 60-day SEP from their HRA eligibility date to enroll in or change an individual health plan.
A change in HRA affordability or offer terms that affects marketplace subsidy eligibility
Other qualifying changes
Gaining U.S. citizenship or lawful presence status
Release from incarceration
A change in income or household size that affects subsidy eligibility
A plan or issuer violation of its contract
An exceptional circumstance (natural disaster, serious medical condition, etc.) recognized by the exchange
If you do have a QLE you can shop for 60 days from the date of the event.