Special Enrollment Period is the health insurance period that lasts for most of the year (February 1- October 31 for 2017) and requires applicants to have a qualifying event and provide documentation of the event in order to apply for health insurance.
If you qualify for an SEP, you usually have up to 60 days following the event to enroll in a plan. If you miss that window, you have to wait until the next Open Enrollment Period to apply.
However, you can enroll in Medicaid and the Children’s Health Insurance Plan (CHIP) any time of year, whether you qualify for a Special Enrollment Period or not.
The Special Enrollment Period was created through the Affordable Care Act, primarily as a compromise in issuing the mandate that health insurance companies can no longer deny individuals coverage for preexisting conditions. In other words, individuals are guaranteed coverage regardless of their health status.
If individuals could simply start and stop coverage whenever they wanted, many people would simply wait until they got sick or required expensive medical care before buying insurance. That is why the government has limited the time to purchase health insurance without any qualifying event up to 3 months out of the year (November 1st - January 31st in 2016, November 1st - December 15th, 2017).
If you don’t have a “qualifying event,” you will not be able to purchase until the next Open Enrollment, which will be from November 1, 2017 - December 15, 2017.