For computation of accrued benefit derived from employee contributions to a defined contribution plan or from voluntary employee contributions to a defined benefit plan, see paragraph (b) of this section. For computation of accrued benefit derived from mandatory employee contributions to a defined benefit plan, see paragraph (c) of this section.
For purposes of this subparagraph, contributions include all amounts which are contributed to the plan even if such amounts are used to provide ancillary benefits, such as incidental life insurance, health insurance, or death benefits, and withdrawals include only amounts distributed to the employee and do not reflect the cost of any death benefits under the plan.
For example, if under section 1017 of the Employee Retirement Income Security Act of 1974, section 411(a)(2) of the Code applies for plan years beginning after December 31, 1975, and for plan years beginning before 1975, the plan provided for 3 percent interest on employee contributions, an employee's accumulated contributions would be computed by crediting interest at the rate provided by the plan (3 percent) for plan years beginning before 1976 and by crediting interest at the rate of 5 percent (or another rate prescribed under section 411(c)(2)(D)) thereafter. Section 1017 of the Employee Retirement Income Security Act of 1974 and § 1.411(a)-2 provide the effective dates for the application of section 411(a)(2).
26 C.F.R. §1.411(c)-1
Sec. 411 (88 Stat. 901; 26 U.S.C. 411 )