A payment or series of payments made under the circumstances described in the preceding sentence is excluded from "wages" even if made pursuant to an incentive compensation plan which also provides for the making of other types of payments. However, any payment or series of payments which would have been paid if the employee's relationship had not been terminated is not excluded from "wages" under this section and section 3306(b)(10). For example, lump-sum payments for unused vacation time or a final paycheck received after retirement are payments which the employee would have received whether or not he retired and therefore are not excluded from "wages." Further, if any payment is made upon or after termination of employment for any reason other than those set out in paragraphs (a)(1), (2), and (3) of this section such payment is not excludable from "wages" by this section. For example, if a pension plan provides for retirement upon disability, completion of 30 years of service, or attainment of age 65, and if an employee who is not disabled retires at age 61 after 30 years of service, none of the retirement payments made to the employee under the pension plan (including any made after he is 65) is excludable from "wages" under this section. However, if the pension plan had conditioned retirement after 30 years of service upon attainment of age 60, all of the retirement payments would have been excludable.
Example. A, an employee, receives a salary of $1,500 a month, payable on the 5th day of the month following the month for which the salary is earned. A's employer has established an incentive compensation plan for a class of his employees, including A, providing for the payment of deferred compensation on termination of employment, including termination upon an employee's death, retirement at age 65 (the retirement age specified in the plan), or retirement for disability. On March 1, 1973, A attains the age of 65 and retires. On March 5, 1973, A receives $5,500 from his employer of which $1,500 represents A's salary for services he performed in February 1973, and $4,000 represents incentive compensation paid under the employer's plan. The amount of $4,000 is excluded from "wages" under this section. The amount of $1,500 is not excluded from "wages" under this section.
26 C.F.R. §31.3306(b)(10)-1