This November 1 – December 15 window applies to individual health insurance shopping (marketplace open enrollment). If you're an employer asking when welcome emails or enrollment notices go out to your employees, that timing is based on your own plan's eligibility date, not this calendar window — see Scheduling Welcome Emails.
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. The December 15 deadline is firm and does not change based on the day of the week.
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 Some states extend Open Enrollment through January 15 or January 31, with coverage starting February 1 for plans selected during these periods. States offering extended periods include Alaska, California, Colorado, Georgia, Kentucky, Maine, Massachusetts, Minnesota, Nevada, New Jersey, New York, Pennsylvania, Rhode Island, Washington, Washington, D.C., and Virginia.
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. For example, if an employee loses coverage on December 31, they qualify for a Special Enrollment Period starting that date, allowing them to enroll beyond the standard deadlines.