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How is Illinois base income figured?
Your Illinois income includes the adjusted gross income (AGI) amount figured on your federal return, plus any additional income that must be added to your AGI. Some of your income may be subtracted when figuring your Illinois base income. For more information, see the Step-by-Step instructions. You should follow the federal law concerning passive activity income and losses. You are not required to refigure your federal passive activity losses. Also, federal law will govern the taxation of income from community property sources in the case of spouses who are residents of different states and who file separate returns.