For example, if an employee leaves employment on April 15, 2023, and 2023 is the first year the plan was in effect, the determination may be based upon the contributions of the employer and the employees during the period beginning with January 1 and ending with April 15, or during the month of March, or during the quarter consisting of January, February, and March.
1. Treas. Reg. § 1.105-11(i).