Illinois Administrative Code
Title 86 - REVENUE
Part 100 - INCOME TAX
Subpart A - TAX IMPOSED
Section 100.2050 - Net Income (IITA Section 202)

a) A taxpayer's net income under the IITA is that portion of the taxpayer's base income (determined under IITA Section 203) for the taxable year that is allocable or apportionable to Illinois under the provisions of Article 3 of the IITA, less the Illinois net loss deduction allowed by IITA Section 207 and the exemptionsallowed by IITA Section 204 and Section 100.2055. (IITA Section 202) In computing net income, any Illinois net operating loss deduction shall be subtracted before the subtraction for the exemptions.

b) For tax years ending on or after December 31, 1986, net income for income tax (IITA Section 201(a) and (b)) and for replacement tax (IITA Section 201(c) and (d)) are identical amounts. For prior tax years, the net income amount for replacement tax was usually a greater amount than net income for income tax. For purposes of the net loss deduction that may be subtracted from net income in those prior years, the amount deductible for income tax purposes shall govern, and the amount that may be deducted for replacement tax purposes in a given tax year shall be the same amount as may be deducted for income tax purposes.