Treas. Reg. § 1.402(g)-2

(a) General rule. Under section 402(g)(1)(C), in determining the amount of elective deferrals that are includible in gross income under section 402(g) for a catch-up eligible participant (within the meaning of § 1.414(v)-1(g)), the otherwise applicable dollar limit under section 402(g)(1)(B) (as increased under section 402(g)(7), to the extent applicable) shall be further increased by the applicable dollar catch-up limit as set forth under § 1.414(v)-1(c)(2).

(b) Participants in multiple plans. Paragraph (a) of this section applies without regard to whether the applicable employer plans (within the meaning of section 414(v)(6)) treat the elective deferrals as catch-up contributions. Thus, a catch-up eligible participant who makes elective deferrals under applicable employer plans of two or more employers that in total exceed the applicable dollar amount under section 402(g)(1) by an amount that does not exceed the applicable dollar catch-up limit under either plan may exclude the elective deferrals from gross income, even if neither applicable employer plan treats those elective deferrals as catch-up contributions.

(c) Effective date