This paper discusses actuarial gains and losses differentiated by their aggregate-level components, i.e., Pension Benefit Obligations (PBOs) of actuarial valuations. One of the most important aspects when evaluating a defined benefit plan is to determine the magnitude of the actuarial gains/losses and to know the origin or source that generates them. The idea is to break down the actuarial total Gain or Loss into its parts. It is important to know how much corresponds to the experience of the plan and regarding the change of assumptions, in turn, in the latter it is important to know the changes in the economic part and in the demographic part. In the change of economic assumptions, the effect of the rate of change of wages and that of the rate of change of interest can be decomposed to discount obligations.