Your Illinois filing period is the same as your federal filing period. We will assume that you are filing your Form IL-1040 for calendar year 2017 unless you indicate a different filing period in the space provided at the top of the return. The due date for calendar year filers is April 17, 2018.
We grant an automatic six-month extension of time to file your return. If you receive a federal extension of more than six months, you are automatically allowed that extension for Illinois. These extensions do not grant you an extension of time to pay any tax you owe. If you determine that you will owe tax, you must use Form IL-505-I, Automatic Extension Payment for Individuals, to pay any tax you owe to avoid penalty and interest on tax not paid by April 17, 2018.
MyTax Illinois is an easy way to pay your IL-505-I payment. If you do not expect to owe tax, you do not have to do anything.