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Menstrual cycle tracking applications are currently among the most widely used devices in France for quantifying the self. Based on a review of the international literature and 21 interviews with young women, this article aims to shed light on the origins and contemporary uses of these applications. Drawing on a socio-historical review that situates them both in the tradition of fertility awareness methods and the emergence of ‘FemTech’, it examines the choice of application, the intensity of its use, and the effects it may have on the user. The article highlights the paradoxically secondary importance of application reliability and data security. It distinguishes between two types of use, restricted and extended, which age and social position help to explain, and it reveals the emergence of a ‘menstrual consciousness’ on three levels (description, interpretation, legitimization) among the most frequent users. Based on a subject related to sexual and reproductive health, the article thus offers a contribution to the sociology of quantification and that of techniques.