This paper deals with the problem of modelling in a formal way the concept of excessprofit, also known as residual income. A common idea is that excess profit is an unequivocalconcept, being the diference between profit and costs, where all types of costs are taken into account, included the opportunity cost, i.e. the profit the entrepreneur would obtain if she invested in another business. This paper aims at showing that this diference is not univocal and that diferent approaches may be followed to give voice to such a notion. It turns out that two diferent interpretations are possible. The one existing in the literature is well described by Preinrich (1938), Edwards and Bell (1961) and, more recently, by Peasnell (1981, 1982) in the accounting literature and by Stewart (1991) in the value-based management literature. The interpretation here provided gives rise to a diferent way of modelling the notion of excess profit. While the existing models are tied to the financial literature, the model here presented is more akin to a microeconomic perspective. The paper focuses on the formal relations among the various models and necessary and sufficient conditions are provided for the integration of all models in the systemic framework here adopted. Furthermore, it shows that the systemic paradigm enjoys an aggregation property which makes residual incomes aggregate in a value sense and enables one to reduce forecasting errors in valuation.
