As soon as practicable after a tax return is filed, the Illinois Department of Revenue (“IL-DOR”) shall examine the tax return to determine the correct amount of tax. If the IL-DOR finds that the amount of tax shown on the tax return is less than the correct amount, then a Notice of Deficiency (“NOD”), which shall set forth the amount of the tax, penalties, and interest, proposed to be assessed, shall be issued to the taxpayer.
If no tax return is filed, then the IL-DOR shall determine the amount of tax due, based on the best information available, and then a NOD, which shall set forth the amount of tax, penalties, and interest, proposed to be assessed, shall be issued to the taxpayer.
A NOD shall set forth the adjustments giving rise to the proposed assessment as well as the reasoning behind those adjustments.