A transfer of legal or equitable title to or rental of property, whether real, personal, or mixed, tangible or intangible, or the performance of services, or a combination thereof, made or engaged in, or caused to be made or engaged in, whether in intrastate, interstate, or foreign commerce, with the object of gain, benefit, or advantage, whether direct or indirect, to the taxpayer or to others, but does not include the services rendered by an employee to his or her employer or services as a director of a corporation. Although an activity of a taxpayer may be incidental to another or to other of his or her business activities, each activity shall be considered to be business engaged in within the meaning of this act. [MCL 208.1105.]

Thus, unless expressly excluded, business income will generally include income derived from any transaction included in the taxpayer's federal taxable income, including "casual transactions" or "isolated sales" that may have been excluded under the SBT.

However, the MBT does exclude certain personal transactions from business income. In particular:

For an individual, estate, partnership organized exclusively for estate or gift planning purposes, or trust organized exclusively for estate or gift planning purposes, business income is that part of federal taxable income derived from transactions, activities, and sources in the regular course of the taxpayer's trade or business. . . ." [MCL 208.1105.]

In other words, for individuals, estates, and certain partnerships and trusts, business income excludes income derived outside the regular course of the taxpayer's trade or business.