Michigan Compiled Laws, Chapter 206. Income Tax Act of 1967 § 206.661

Sec. 661. (1) Except as otherwise provided in this part, the tax base established under this part shall be apportioned in accordance with this chapter.

(2) The tax base of a taxpayer whose business activities are confined solely to this state shall be allocated to this state. The tax base of a taxpayer whose business activities are subject to tax both within and outside of this state shall be apportioned to this state by multiplying the tax base by the sales factor calculated under section 663.  1 For a taxpayer that has a direct, or indirect through 1 or more other flow-through entities, ownership interest or beneficial interest in a flow-through entity, the taxpayer's business income that is directly attributable to the business activity of the flow-through entity shall be apportioned to this state using an apportionment factor determined under section 663 based on the business activity of the flow-through entity unless the flow-through entity is unitary with the taxpayer for apportionment purposes as provided under section 663.

(3) A taxpayer is subject to tax in another state in either of the following circumstances: