Activity rules
Activity rules(i) In general. The basic activity rule treats each undertaking in which a taxpayer owns an interest as a separate activity of the taxpayer (see paragraph (b)(1) of this section). In the case of trade or business undertakings, professional service undertakings, and rental real estate undertakings, additional rules may either require or permit the aggregation of two or more undertakings into a single activity.
(i)In general.The basic activity rule treats each undertaking in which a taxpayer owns an interest as a separate activity of the taxpayer (seeparagraph (b)(1)of this section). In the case of trade or business undertakings, professional service undertakings, and rental real estate undertakings, additional rules may either require or permit the aggregation of two or more undertakings into a single activity.