20 C.F.R. § 225.11 – Tier I PIA.

(a) General. The Tier I PIA is used in computing an employee, spouse or divorced spouse tier I amount. Except for the cases described in paragraphs (b) through (d) of this section, a Tier I PIA is determined under sections 215 and 223 of the Social Security Act. Railroad and Social Security earnings are included in the calculation of a Tier I PIA.
(b) Employee attains age 60 and/or acquires 30 years of service after June 30, 1984. When an employee is entitled to an age and service annuity before the month of attaining age 62, as explained in part 216 of this chapter, the following Railroad Retirement Act rules apply in addition to those in § 225.11(a) in computing the Tier I PIA.
1. (1) Four months before the first full month the employee is age 62, the Average Indexed Monthly Earnings is determined as if the employee's eligibility year were the year the annuity began.
2. (2) The benefit computation years used in computing the Tier I PIA are based on the date of the employee's actual attainment of age 62.
3. (3) The Tier I PIA is adjusted when the employee reaches age 62 to use the year in which the employee attains age 62 as the eligibility year.
4. (4) Cost-of-living increases and recomputations apply after the employee attains age 62.
(c) Employee attains age 60 and acquires 30 years of service before July 1, 1984. For purposes of determining the benefit computation years to be used in computing the Tier I PIA for an employee who is age 60 through 64, and who both has 30 years of service and attains age 60 prior to July 1, 1984, the employee is considered to be age 65 when the age and service annuity begins. For purposes of computing the Average Indexed Monthly Earnings, the eligibility year is the year the annuity begins or age 62, if earlier. Cost-of-living increases are paid from the year the annuity begins. Recomputations are paid after the employee actually attain age 62.
(d) Disability annuity. When an employee is entitled to a disability annuity, as explained in subpart B of part 216 of this chapter, the following Railroad Retirement Act rule applies in addition to those in § 225.11(a) in computing the Tier I PIA. The Tier I PIA is computed as if the employee were 62 years old on the date, as determined by the Board, of onset of disability, if the employee is under age 62 on that date.