This essay examines the importance of an accounting culture for the rise of marginalism in Victorian England. I trace the use of accounting tools in family and private life to fend off uncertainties in the market and to enhance moral control of the self, examining the use of diaristic accounting for two Victorians, George Eliot and William Stanley Jevons, in more detail. The philosopher of mind Alexander Bain recommended the use of mercantile accounting tools, Benjamin Franklin's moral algebra in particular, to harness the mind against emotional and myopic decision making. Bain's recommendation was critically tested by Eliot in Middlemarch and used by Jevons to naturalize the mind's balancing of pleasures and pains as an algebra of feelings. Washing out all differences between reason and emotion, Jevons's theory of pleasure and pain became foundational for the economists' theory of utility. Contemporary critics of rational choice theory take this naturalized image of the economic agent as its bogeyman, ignoring the social infrastructure that brought this agent, thinking as a merchant, into existence. The idea that we calculate captures a sociohistorical reality, rather than a physiological or psychological fact.