The Department of Revenue Services said an error for some property tax credit claims may have resulted in a higher credit to taxpayer's liability.
For certain filing statuses for 2015, the miscalculation has resulted in up to $12 million in underpayments of personal income taxes across about 120,000 income taxpayers.
The DRS said affected taxpayers have already received refunds or will be notified in writing. Anyone who underpaid will be billed without penalty, the DRS said.
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"When we make a mistake, we own it and fix it immediately," Kevin Sullivan, commissioner of the DRS, said in a statement. "This year the DRS will process 1.6 million resident state income returns and while this affects a relatively small number of income taxpayers, I apologize for our error and the inconvenience to those taxpayers."