The present article explores how cycles are brought into being through the practices and affordances involved in period-tracking with apps. Based on thirteen in-depth semi-structured interviews with period-tracking app users living in the Netherlands, it expands on literature discussing the relationship between embodiment, apps, and quantification. The contributions of this article are two-fold. Theoretically, it argues for the use of Karen Barad’s notion of apparatus to understand how bodies are (re)configured in relation to self-tracking technologies (1998). Empirically, it exposes how bodies emerge in localized period-tracking practices, within material-semiotic arrangements that both resist and reproduce cultural ideals about menstruating bodies. Period-tracking with apps, this study finds, brings the body’s interior processes into being in a “systematic” way, (re)configuring the cycle as either a series of phases or an interval with a certain (normative) duration. In all cases, periodtracking with apps becomes a means for users to access their internal body and to materialize the invisible processes of the cycle in ways that can be acted upon.