Some individuals and families who purchased their health insurance through a government exchange like Healthcare.gov or Covered California may be subject to the Penalty for Underpayment of Estimated Tax. The underpayment penalty is triggered when the federal income tax due is less than 90% of the previous year’s tax liability. If a tax household received thousands of dollars of the monthly Advance Premium Tax Credit (APTC) subsidy to lower their health insurance premiums, but earned too much taxable income to actually qualify for the Premium Tax Credit, the tax payer has to repay the entire subsidy. This repayment amount could easily trigger the underpayment penalty.