Obamacare's individual mandate generated about $1.5 billion from about 7.5 million people during its first year in existence.

That figure is about 1 million more than previously estimated would pay the mandate penalty for not getting health insurance in 2014.

The Internal Revenue Service offered details on the penalties in a letter to Congress Friday.

Under the individual mandate, if taxpayers didn't have health insurance in 2014, they would have to pay 1 percent of their yearly incomes, or $95 per person plus nearly $50 per child.

However, low-income taxpayers get an exemption. The IRS found that about 12 million taxpayers claimed that exemption, according to the letter from IRS Commissioner John Koskinen.

The agency also found that about 300,000 low-income taxpayers paid the penalty when they could have claimed an exemption. Koskinen said the agency is reaching out to the taxpayers to inform them that they could get out of the penalty by amending their return.

"Generally, taxpayers have three years to file amended returns," he said.

The penalty climbs next year to $325 per person, or 2 percent of yearly income.