While tax prep giant H&R Block initially estimated that half of ObamaCare (ACA) subsidy recipients would have to pay money back to the IRS, the final tally is even worse:
Almost two-thirds of tax filers who received insurance via the state or federal insurance marketplaces had to pay back an average of $729 of the Advance Premium Tax Credit (APTC), cutting their potential refund by almost one-third, according to analysis of filing data by H&R Block. [H&R Block]
For the rest of H&R Block customers, tax season was a little less traumatic: About one quarter of insurance subsidy recipients saw an increase in their tax refunds, while 13 percent saw no change.
The confusion has occurred because — on top of the complexity the ACA adds to the tax code — estimating income in advance to calculate how big an insurance subsidy should be is difficult for non-salaried workers. As Timothy Jost, a Washington and Lee University law professor, explains, "If you’re a person who is a waitress or worked for a landscape company and you're asked how much money you're going to make, you're really just throwing a dart at the board."