In identifying as the core of Leibniz's thought the problem of calculation, Heidegger grasps something that is actually true, but at the same time he allows room for misunderstandings. We must, indeed, explain: what does calculation really mean for Leibniz? And what does Heidegger mean by the expression "calculating thought"? In a preliminary way, calculation represents the pointe of Leibniz's reflections: the lapidary nature of the sentence "Cum Deus calculat [...] fit mundus" is a direct confirmation of this, but it also shifts the meaning of calculation from the plane of mathematical operations to the more original sphere of a metaphysics of calculation, as part of the set of harmonious activities of the monadological cosmos. The image of calculation must be absorbed in a linguistic aggregate that aims at unifying scientia and pietas, mathematicalnatural knowledge and the intuition of the monadological order of the world. Calculation is overturned in the combinatoria, which is one of the pillars of Leibniz's thought; mathematics relates to imagination, and metaphysics regards the most abstract things. The point of arrival of monadology is, in fact, a reflection (the opposite of deduction) of God in the monads. This theoretical conversion affects the linguistic presuppositions and the traditional limits of general metaphysics.