Michigan Compiled Laws, Chapter 206. Income Tax Act of 1967 § 206.663

Sec. 663. (1) Except as otherwise provided in subsection (2) and section 669,  1 the sales factor is a fraction, the numerator of which is the total sales of the taxpayer in this state during the tax year and the denominator of which is the total sales of the taxpayer everywhere during the tax year. The numerator of a taxpayer shall include its proportionate share of the total sales in this state of a flow-through entity that is unitary with the taxpayer. The denominator of a taxpayer shall include its proportionate share of the total sales everywhere of a flow-through entity that is unitary with the taxpayer. A flow-through entity is unitary with a taxpayer when that taxpayer owns or controls, directly or indirectly, more than 50% of the ownership interests with voting rights or ownership interests that confer comparable rights to voting rights of the flow-through entity, and that has business activities or operations which result in a flow of value between the taxpayer and the flow-through entity, or between the flow-through entity and another flow-through entity unitary with the taxpayer, or has business activities or operations that are integrated with, are dependent upon, or contribute to each other.

(2) Except as otherwise provided under this subsection, for a taxpayer that is a unitary business group, sales include sales in this state of every person included in the unitary business group without regard to whether the person has nexus in this state. Sales between persons included in a unitary business group must be eliminated in calculating the sales factor. Sales between a taxpayer and a flow-through entity unitary with that taxpayer shall, to the extent of the taxpayer's interest in the flow-through entity, be eliminated in calculating the sales factor.Sales between a flow-through entity unitary with a taxpayer and another flow-through entity unitary with that same taxpayer shall, to the extent of the taxpayer's interest in the selling flow-through entity, be eliminated in calculating the sales factor.

(3) It is the intent of the legislature that the tax base of a taxpayer is apportioned to this state by multiplying the tax base by the sales factor multiplied by 100% and that apportionment shall not be based on property, payroll, or any other factor notwithstanding section 1 of 1969 PA 343, MCL 205.581.