Under the federal Affordable Care Act, most people are required to have insurance or face a tax penalty.
The state-run health exchange, which launched in October 2013, offers sliding-scale subsidies for private coverage to people with no access to health care on the job and directs low-income people to Medi-Cal, the state's health program for the poor.
As a result, California has reduced the number of uninsured by millions. Sunday's deadline does not affect low- and no-cost Medi-Cal insurance enrollment, which continues year-round through the Covered California website.
Fines are also going up for people who remain uninsured in 2016. The minimum penalty is $695 for someone who's uninsured the full year.
Anyone who starts the application process by Sunday has until Feb. 6 to submit their application.
Exchange officials are encouraging people to contact service representatives, enrollment counselors and certified insurance agents to help them complete the process.
An enrollment drive is also being held at the Rose Bowl in Pasadena from 10 a.m. to midnight Sunday.
Visit http://www.coveredca.com or call (800) 300-1506 for more information.