If you are required to file an Illinois return, the return must be filed in a timely manner, regardless of net income or loss. If the loss return calculates an overpayment for which you expect to receive a refund or request a credit carry forward, you must file the loss return within 3 years of the extended due date of the loss return to receive a refund or credit carry forward.
EXAMPLE: You claim a Net Loss Deduction on your December 2021 Form IL-1120. The loss you are claiming is from your December 2015 reporting period; however, you did not file your December 2015 Form IL-1120 until March 2021. Your December 2015 Form IL-1120 calculates a net loss and claims an overpayment from your December 2015 reporting period which you request as a refund. The loss generated on your December 2015 return is available to be claimed on your December 2021 Form IL-1120; however, the refund claimed, due to the overpayment from the December 2015 reporting period, is unavailable to be refunded or applied toward a subsequent reporting period because your December 2015 reporting period was filed more than three years from the extended due date of the original return.