By notification if you mean the turbotax software indicates you have an underpayment, then it sounds like you got hit by the new tax laws for 2018. Meaning the underpayment, means for 2018 you did not have enough taxes held from your paycheck or via estimated payments. So now you might get hit with an underpayment penalty for 2018. TT should walk you through the steps to get an exemption if you were impacted by the new tax rules. The big changes were less money was held from you paycheck, state and local income tax deductions are now limited to $10,000 (assumes you itemized deductions), and they removed the personal exemptions of about $4,050 for yourself and spouse.
