Tax Day is less than a month away, but many Americans are unaware Obamacare's tax penalty goes into effect this year — or that they have extra time to sign up for coverage.

A Kaiser Family Foundation poll released Thursday found that while slightly more than half of respondents were aware the penalty kicks in this year, one in five think it goes into effect next year, roughly one in six say they don't know when it goes into effect, and one in 10 believe it was rolled out last year.

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If people are penalized, it's because they lacked health coverage last year and didn't qualify for an exemption from the healthcare law's requirement to buy insurance. Even if they buy coverage this year, that wouldn't erase the penalty they'd have to pay for lacking coverage last year.

The Obama administration is still providing them with an extra signup period that started on Sunday and lasts until April 15. But officials have acknowledged there are challenges in getting that key demographic to sign up.

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"We do know that are some people … that didn't learn about open enrollment and didn't learn about the requirement to have coverage until they paid their taxes," Andy Slavitt, principle deputy administrator at the Centers for Medicare and Medicaid Services, said last week.

"For many people, this will be the first time they discover they have the opportunity to get coverage for themselves and their families," he added.

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A majority of Americans think the extra signup period is a good idea, according to the Kaiser poll. About six in 10 respondents said people should get another chance to sign up to avoid paying a penalty next year, while three in 10 said it's unfair to those who enrolled during the regular enrollment season that ended Feb. 15.

A McKinsey study this month found that 41 percent of uninsured Americans are unaware of the tax penalty, which will equal either $95 or 1 percent of income above the filing threshold — about $400 for a person earning $50,000.

And a survey by the tax preparation firm Jackson Hewitt — which sees itself as playing an instrumental role in encouraging people to get insured — found that nearly half of Americans don't know they have a second chance to sign up for coverage.

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Another 27 percent said they don't know whether the enrollment period has expired or not.

"Our survey results clearly show that Americans don't know that many can still sign up for health insurance and avoid the tax penalty this year," Jackson Hewitt CEO David Prokupek said.