You might have missed that big Obamacare enrollment deadline you heard about last week — but there's a good chance you can still sign up for an Obamacare plan.

Nearly half of the U.S. population lives in an area where the final deadline for signing up for Obamacare has yet to hit, or where there are special exceptions to the deadline for this month.

But widespread confusion about deadlines for selecting an individual insurance plan this year is putting people at risk of missing out on a last chance of getting health coverage for 2018.

"The vast majority of people did not know the deadlines in their state," said Karen Pollitz, a senior fellow at the Kaiser Family Foundation, a leading health policy research group.

That confusion is understandable, since there's no single deadline this sign-up season in the entire United States, and because the deadline in large areas of the country was cut in half from last season.

But nine states and the District of Columbia, which all run their own Obamacare marketplaces, have separate upcoming deadlines, falling between this Friday and Jan. 31.

"Oh, it's messy!" said Charles Gaba, who runs the Obamacare tracking site ACASignups.net, and who in recent days has posted a flurry of news updates about areas where people can still enroll.

Gaba has estimated that about 49 percent of the U.S. population lives in an area where the final sign-up deadline has yet to pass for 2018 coverage or where residents can sign up outside of a passed deadline.

But he said federal health officials could have done a much better job at alerting people in many areas to their eligibility for signing up outside of an earlier deadline.

The Kaiser Family Foundation published an updated map on the deadlines Tuesday afternoon, reflecting new information.