A special enrollment period allows you to enroll in an ACA-compliant plan (on or off-exchange) if you have a qualifying life event. Normally, coverage is only available for purchase during the annual open enrollment period, but a special enrollment period allows people to sign up for coverage outside of that annual window, as long as they have a qualifying event.
In the case of involuntary loss of coverage, the special enrollment period begins in advance of the loss of coverage so that enrollees can purchase a new plan with no gap in coverage. The rest of the qualifying events trigger a special enrollment period that begins on the date of the qualifying event and continue for 60 days. In most cases, coverage must be selected by the 15th of the month in order to be effective the first of the following month, but there are some exceptions (birth or adoption of a child, marriage, and involuntary loss of coverage) that have different rules for coverage effective dates.
If you do not have a qualifying event that triggers a special enrollment period, you can only enroll in an ACA-compliant plan (on or off-exchange) during the regular annual open enrollment period.
There are also special enrollment periods for employer-sponsored plans, during which you can enroll in your employer’s plan outside of their open enrollment period. Most of the qualifying life events that apply to employer-sponsored plans are similar to the qualifying events that trigger a special enrollment period in the individual market, but there are some differences.