Conn. Gen. Stat. § 12-687
Timing of payments. Late payments.
(b) Where any tax payment is required to be made by electronic funds transfer, such payment shall be treated as a tax payment not made in a timely manner if the electronic funds transfer for the amount of the tax payment is not initiated on or before the due date thereof. (1) For periods ending prior to December 31, 2019, any tax payment treated under this subsection as a tax payment not made in a timely manner shall be subject to interest in accordance with the applicable provisions of the general statutes, and a penalty that shall be equal to two per cent of the tax payment required to be made by electronic funds transfer, if such failure to pay by electronic funds transfer is for not more than five days, five per cent of the tax payment required to be made by electronic funds transfer, if such failure to pay by electronic funds transfer is for more than five days but not more than fifteen days, and ten per cent of the tax payment required to be made by electronic funds transfer, if such failure to pay by electronic funds transfer is for more than fifteen days; and (2) for periods ending on and after December 31, 2019, any tax payment treated under this subsection as a tax payment not made in a timely manner shall be subject to interest and penalty in accordance with the applicable provisions of the general statutes.