Subsidy, what subsidy? Millions unaware of their Obamacare aid

They're Obamacare-d for, and they're clueless about it.

Nearly 40 percent of Obamacare enrollees who receive federal financial assistance to help pay for insurance sold through HealthCare.gov don't even know they're getting any such aid, a survey stunningly found.

That finding means that about 2.1 million people—at the very least—are unaware that they stand to lose thousands of dollars worth of aid that makes their health insurance affordable if the Supreme Court upholds a new court decision that said such subsidies are illegal under the Affordable Care Act.

"There are clearly people out there who would be significantly affected by the Halbig decision, but probably don't even realize it," said Kaiser Family Foundation Senior Vice President Larry Levitt, referring to the case known as Halbig v. Burwell.

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"These people would lose the subsidies they're not even aware they're getting," Levitt said.

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Buried in a Kaiser Family Foundation survey in June was the finding that just 49 percent of people who signed up for insurance via HealthCare.gov said they are getting subsidies to help pay for their premiums.

That's despite the fact that the percentage of HealthCare.gov enrollees who actually get those subsidies is actually much higher: 86 percent of enrollees are not paying their insurance plan's full sticker price because the federal government is footing some or much of the bill.

Levitt said that even people who know they are getting subsidies for HealthCare.gov plans are unlikely to know that a Supreme Court decision in the Halbig case could render that assistance illegal.

Such a decision would affect only subsidies issued through a federal insurance marketplace—such as HealthCare.gov—not the subsidies issued through one of 15 Obamacare exchanges run by an individual state or the District of Columbia. About 4.7 million people receive subsidies for their HealthCare.gov plans, which are sold in 36 states.

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A recent Avalere Health analysis said that for those people, their monthly insurance premium prices would rise an average of 76 percent if the subsidies were taken away.

In a controversial ruling last Tuesday, a federal appeals court panel in Washington, D.C., said that the Affordable Care Act, as explicitly written, only authorizes subsidies to be issued through state-run exchanges.

The Obama administration and another federal appeals circuit's panel disagrees with that decision, saying the ACA allows subsidies for HealthCare.gov enrollees. For now, those subsidies remain in effect.

But if the administration doesn't persuade the full D.C. appeals circuit to reverse its panel's ruling, the case would go to the Supreme Court, which could invalidate the HealthCare.gov subsidies.

"This is a major, major threat to the ACA. If Halbig prevails, millions of people will lose access to subsidies," Levitt said.

Still, he said, "I can't imagine that the average person grasps what's going on with this Halbig case."

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Levitt noted that while Obamacare enrollees "are generally happy with their plans," as detailed in the June survey by Kaiser, "there are still concerns about their affordability."

"Those [concerns] would be even more severe if their subsidies got taken away," he said.

Currently, people whose income is between 100 percent to 400 percent of the federal poverty level are entitled to taxpayer-funded subsidies from the federal government to help pay for monthly premiums of plans sold on a health insurance exchange run by either a state or the federal government. For an individuals, that is between about $11,670 to $46,680 annually, and for a family of four, it's between about $23,850 to $95,400 per year.

A total of 86 percent of the 5.45 million people who signed up for insurance sold on HealthCare.gov qualified for a premium subsidy.

Those subsides are, on average, very generous. According to the U.S. Health and Human Services, nearly 70 percent of people receiving Obamacare subsidies are paying $100 or less per month in premiums for their insurance, while 46 percent are paying $50 or less per month.

Despite that, the Kaiser survey showed, a large percentage of people were unaware they received subsidies, even though it often meant the difference between a plan costing them hundreds of dollars per month, versus a bill in the double digits.

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The finding that only 49 percent of all federal exchange enrollees believed they were getting a subsidy had a fairly large margin of error, of plus or minus 8 percent. But Levitt noted that while the true figure "may be somewhat more or somewhat less...still there's lots of people that don't realize they're getting subsidies."

The finding is surprising, he said, because "it's not easy to apply for subsidies, it was a pretty elaborate process."

"You've got give a lot of private information about your income and family circumstances," he said. "For someone to go through the process and not even understand that they were getting a subsidy is a little surprising."

But, he said, "We know people are very confused about health insurance."

Levitt said someone who received help in applying for Obamacare from a so-called navigator or other person may not have fully grasped all of the steps of the process, and instead just focused on the bottom line of the amount they would be obligated to pay per month once the application was completed.

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"They got a bill from the insurer, and they may not realize they're not paying the full price of the insurance," Levitt said.

"There's not a monthly reminder of the fact that you're not paying a full premium and are getting a subsidy."

By CNBC's Dan Mangan.