20 C.F.R. § 226.30 : Employees' Benefits — RAILROAD RETIREMENT BOARD — REGULATIONS UNDER THE RAILROAD RETIREMENT ACT — COMPUTING EMPLOYEE, SPOUSE, AND DIVORCED SPOUSE ANNUITIES — COMPUTING A SPOUSE OR DIVORCED SPOUSE ANNUITY — Spouse or divorced spouse tier I

(a) General. The tier I of a spouse or divorced spouse annuity is an amount similar to the social security benefit the spouse or divorced spouse would receive based on the employee's combined railroad and social security earnings. In the case of an employee who retires before age 62 with 30 years of service, the spouse tier I is simply 50% of the employee tier I until the first month throughout which both the employee and spouse are age 62 at which time the tier I is an amount similar to the social security benefit on the employee's combined railroad and social security earnings.
(b) Reduction for other disability benefits. The spouse or divorced spouse tier I may be adjusted for other disability benefits received by a disabled employee, as shown in §§ 226.70-226.74 of this part.
(c) Reduction for government pension. The amount in paragraphs (a) or (b) of this section is reduced (but not below zero) by the amount of any government pension payable on the spouse's or divorced spouse's earnings record, as described in §226.31 of this part.
(d) Rounding. The last tier I rate from paragraph (a), (b) or (c) of this section, if not a multiple of $1, is rounded to the next lower multiple of $1. However, in cases in which the spouse is in receipt of an age reduced 60/30 annuity or in which the employee with 30 years of service began a disability annuity July 1, 1984, or later, the spouse tier I is not rounded until all reductions have been made. See §226.10(a).
(e) Age reduction. If the spouse or divorced spouse is entitled to a reduced age annuity (see §§216.51 and 216.52 of this chapter), the rounded tier I rate from paragraph (d) of this section is multiplied by a fraction for each month the spouse or divorced spouse is under retirement age on the date the annuity begins. The result is subtracted from the rate from paragraph (d) of this section. At present the fraction is 25/36 of 1% (or 1/144). In the case of an employee with 30 years of service who is awarded a disability annuity on July 1, 1984, or later, where the spouse does not have a child of the employee under age 18 in care, the spouse tier I is reduced for each month the spouse is under retirement age on the date the spouse annuity begins. If the spouse is age 60 or 61, he or she is deemed to be age 62 for purposes of the age reduction. The age reduction is applied before reduction for a government pension.
(f) Reduction for social security benefit. The previous tier I rate, from paragraph (d) or (e) of this section, is reduced by the amount of any monthly benefit payable to the spouse or divorced spouse under title II of the Social Security Act. The social security benefit used to reduce tier I may be an age or disability benefit on the spouse's or divorced spouse's own earnings record, a benefit based on the earnings record of another person, or the total of two types of benefits. The result cannot be less than zero.
(g) Reduction for employee annuity. If the spouse or divorced spouse is entitled to an employee annuity on his or her own wage record, the spouse or divorced spouse tier I is reduced for the spouse's own employee annuity as follows:
(1) Spouse. If either the employee or the spouse had some railroad service before 1975, the previous tier I rate from paragraphs (d) through (f) of this section, whichever applies, is reduced (but not below zero) by the spouse's own employee tier I rate, as computed under §226.10 of this part. If both the employee and spouse began railroad service after 1974, the spouse's total annuity rate, as shown in §226.33, is reduced (but not below zero) by the spouse's own employee total annuity rate, as shown in §226.14. These reductions are effective from the later of the date the employee or spouse annuity begins.
(2) Divorced spouse. The previous tier I rate from paragraphs (d) through (f) of this section, whichever applies, is reduced (but not below zero) by the divorced spouse's own employee total annuity rate as shown in §226.14.

Example: The computation of the spouse tier I may be illustrated as follows: A railroad employee's wife who was born on September 16, 1920, becomes entitled to a spouse annuity on October 1, 1982. She is also entitled to a social security benefit of $190 a month effective October 1, 1982. Her husband's employee tier I PIA is $712.60. The spouse tier I is $356.30 (50 percent of $712.60). This is rounded down to $356. Since she is 35 months under age 65, the present retirement age when the annuity begins, $356 is multiplied by 35/144, to produce an age reduction of $86.53 and a tier I rate after age reduction of $269.47. Her final tier I rate effective October 1, 1982, after reduction for social security benefits, is $79.47 ($269.47 -$190.00).

20 C.F.R. § 226.30