H&R Block has released some telling statistics on how the Affordable Care Act has affected income tax refunds.

The tax preparation giant said 52 percent of consumers who bought health insurance through a federally or state-operated insurance exchange are having to repay an average $530 of the premium tax credit they received from the government to help pay insurance premiums.

The repayment cut their tax refund by an average 17 percent, according to H&R Block's analysis, almost six weeks into the tax-filing season.

The statistics highlight how many Americans could find filing their tax returns especially challenging this year.

For the first time, taxpayers have to state whether they had health insurance through an employer, a health insurance exchange or a private insurance policy in 2014.

For most Americans that will simply mean checking a box on their tax returns to show they had health coverage all year.

But it's a different story for those who didn't have health insurance last year. They could face a tax penalty.

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The average tax penalty for not having health insurance was $172, H&R Block said. That's more than the flat fee of $95 per uncovered adult that many consumers anticipated.

Yet the consumers likely to be the most confused are those who received the premium tax credits. They will have to reconcile the financial assistance received with actual income. This is the part that will trip up many taxpayers.

Most people chose to have the subsidies paid in advance, based on their projected income for 2014. If their actual income was higher because of a raise or new job, they would be entitled to a smaller subsidy and would have to repay the difference, subject to certain limits.

H&R Block expected that most filers wouldn't accurately estimate their 2014 income since many taxpayers relied on 2012 income to estimate their 2014 income at the time of the first open enrollment.

"The average tax refund for these taxpayers was almost $3,100, but it was reduced by $530 due to the tax credit reconciliation process," the firm said.

If H&R Block's numbers are an accurate indication, more taxpayers who bought health insurance from an exchange will be hit with the bad news that they will have to repay a portion or all of their subsidy.

On the other end of the spectrum, H&R Block said that about a third of insurance marketplace enrollees overestimated their 2014 income and got an additional premium tax credit of close to $365 on average.

If you received a tax credit last year, cross your fingers you're in this group.