The felicific calculus was a hypothetical method for calculating the degree or amount of happiness that a specific action is likely to cause. Felicific calculus was introduced by Jeremy Bentham, a Utilitarian, in order to introduce a scientific method for calculating happiness, as happiness is the determining factor of the morality of an action for Utilitarians. Variables, or vectorss included in this calculation include propinquity (closeness) and fecundity (likeliness to produce more happiness).

Critics claim the felicific calculus fails as a moral theory because there is no principle of fairness. For example, according to this theory, it would be moral to torture one person if this would produce an amount of happiness in other people outweighing the unhappiness of the tortured individual. This was arguably remedied by John Stuart Mill.

It has also been argued that the happiness of different people is incommensurable (lacking a basis for comparison), and thus a felicific calculus is impossible in practice.