By Christopher Lutz ( May 30, 2018, 5:29 PM EDT) -- In calculating the Illinois sales factor, Illinois employs both a "throw-back" and "throw-out" rule. Under the throw-back rule, if a sale of tangible personal property originates in Illinois and the taxpayer is not subject to tax in the destination state, the gross receipts from the sale will be "thrown back" to Illinois and will be included in the numerator of the Illinois sales factor. Under the throw-out rule, if a taxpayer is not subject to tax in the state in which its customer receives the taxpayer's services, the gross receipts from the sale of the services will be entirely "thrown out" of the Illinois sales factor and be excluded from the denominator of the factor....