20 CFR 228.2: Tier I and tier II annuity components.

(a) Tier I annuity component. The Tier I annuity component is generally the amount that would have been payable under the Social Security Act if all of the employee's earnings after 1936 under both the railroad retirement system and the social security system had been creditable under the Social Security Act.

(b) Tier II annuity component. The tier II annuity component is the portion of the survivor's annuity which is based on an employee's railroad earnings only. The tier II component of an annuity described in this part is a specified percentage of the employee's actual or anticipated tier II annuity component.