The 2017 Connecticut income tax return (and payments) will be considered timely if filed on Tuesday, April 17, 2018.
In 2018, the due date for filing a Connecticut income tax return (April 15) falls on a Sunday. The next business day is Monday, April 16, which is a legal holiday in the District of Columbia (Emancipation Day). Therefore, for filing purposes the next business day is Tuesday, April 17, 2018.
This change does not affect any other taxes, except use tax and gift tax.