If you are filing as a combined taxpayer, see Illinois Schedule UB,. Specific Instructions for Completing Form IL-1120.Corporations must pay an annual Illinois franchise tax based on the amount of paid-in capital as of the 3rd month before the corporation's anniversary month. Paid-in capital is the total amount of cash that a company has received in exchange for its common or preferred stock issues. Value in excess of Par times the number of shares. (Often called "Additional Paid-in Capital" or "Paid- in Capital in Excess of Par"). Electronically filed returns. The electronic filing threshold for corporate returns required to be filed on or after January 1, 2024,. In the case of sales of capital assets, the fiduciary computes its net capital gain or loss in the normal fashion. Apportionment is the assignment of a portion of a corporation's income tax in a state.