Fertility apps are digital tools for recording menstruation and bodily signs of fertility, with the aim of predicting future ovulation dates. For women trying to conceive, these predictions can be used to time heterosexual intercourse or insemination close to ovulation and thus increase chances of conception. This chapter explores women's use of fertility-tracking apps and the consequences of this for their experiences of trying to conceive in heterosexual relationships. I draw on findings from a thematic analysis of app content and interviews with women in the United Kingdom who had used apps to help them conceive, to show how these apps are often present in the in-between or transitional times and spaces of reproductive life. Apps are used to increase chances of pregnancy, but they are also used to navigate the many uncertainties of trying to conceive. Through a critical engagement with notions of control, anticipation and awareness, I explore how apps shape and are shaped by an increasingly demanding social and cultural context of reproduction.