Tax Facts

3934 / When are trades or businesses under common control?

Updated: October 20, 2026 at 03:26 PM


Under the regulations, trades or businesses are under common control if they constitute a parent-subsidiary group of trades or businesses, a brother-sister group of trades or businesses, or a combined group of trades or businesses. The existence of these groups is determined under rules similar to those discussed in Q 8964 for controlled groups of corporations. “Trades or businesses” include sole proprietorships, partnerships, estates, trusts, and corporations.1





1.  IRC § 414(c); Treas. Reg. §§ 1.414(c)-1, 1.414(c)-2, 1.414(c)-3, 1.414(c)-4.


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