Covered California says more than 416,000 people picked a health care plan last month, and that the total number of people who have applied for coverage and selected a plan is now more than 1,222,000.
The exchange says about 28% of those enrolled are between the ages of 18 and 34. More than 500,000 people have started accounts but not yet completed them.
They have until April 15th.
Officials did meet sign-up goals, but nearly half of Covered California's enrollees may drop their insurance.
Researchers at UC Berkeley estimate 20% of the exchange's customers will leave the program this year because they'll find a job that offers coverage.
Another 20% will see incomes drop to a level that qualifies them for Medi-Cal instead.
This kind of a "churning" process is well-known in the insurance industry and just how many people have actually paid their premiums has become a political issue.
As people move out of Covered California, others will move in. Potentially hundreds of thousands who qualify through a "life event" like divorce or job loss.