Description: This paper gives a mathematical proof of the frequently expressed concept that under the entry age normal method of valuing a retirement plan, the salary scale applies retroactively. That is, it demonstrates that the valuation of a plan assumes that all past contributions to the plan were based on salaries which, when projected by the salary scale, reproduce the present level of income. The concept of retroactivity is also applied to a situation where there is a constant offset such as the social security benefit. In addition, the paper discusses the effect on this liability resulting from an increase in salary in excess of the increase provided by the salary scale and the effect on the liability of certain types of salary-scale changes. From Transactions of Society of Actuaries 1973, Vol. 25, Pt. 1, No. 72AB.