Description: This paper addresses how to explain yearly fluctuations and computed pension cost in terms of deviations of actual from expected experience. It presents a method for deriving gain-an-loss analysis formulas directly from the valuation formulas and shows that the analysis is implicitly defined by the valuation formulas, rather than something which can be considered apart from them. This method can be used to attack both individual and aggregate cost methods and the development of exact analysis formulas provides not only the basis for computation but also valuable insight into the mechanisms by which cost methods adjust computed costs to reflect actual experience.