Conn. Gen. Stat. § 12-645: Date of filing of returns. Exception.

Returns required under this chapter shall be filed on or before the fifteenth day of April following the close of the calendar year except where a gift is made during the calendar year in which the donor dies, the return with respect to such donor shall be filed on or before the last date, including extensions, for filing the estate tax return under chapter 217 with respect to such donor.