20 C.F.R. § 225.1
This part discusses Primary Insurance Amount, which is referred to as PIA throughout this part, and which is an important element in the calculation of any retirement or survivor annuity. There are a number of PIA computations based on different periods, amounts, and types of earnings. However, the formulas for computing any PIA are prescribed in section 215 of the Social Security Act and are described in detail in the regulations of the Social Security Administration ( 20 CFR part 404, subpart C). This part discusses PIA computation formulas and relates them to the PIA's which the Board uses. Descriptions of the majority of PIA's used in computing retirement or survivor annuities under the Railroad Retirement Act are contained in this part. Explanations are included of when delayed retirement credits and cost-of-living increases can be added to the PIA's used by the Board. This part also explains when and how a PIA is recomputed or adjusted. Since these regulations are intended to address annuities currently being awarded, certain PIA's, not used in the computation of annuities awarded after August 13, 1981, are not included in these regulations. Parts 226, 228 and 229 of this chapter explain how PIA's are used in actual annuity computations.
20 C.F.R. §225.1