This paper explores reproductive decision-making among young women in South Africa's informal settlements and considers whether and how agency and social norm theory inform their decisions. Understanding whether, when and how young women make decisions about conception and motherhood is critical for supporting women to avoid unplanned, early motherhood. Qualitative data were collected from 15 young women in informal settlements in eThekwini, South Africa at three time points over 18 months, using in-depth interviews, participant observation and photovoice, and were analysed inductively. When the young women were teenagers and into their early twenties, and had not yet had a child, most paid little attention to whether or not they conceived. This shifted as they grew older and/or after having a first child, at which point many of the women began to express, and sometimes act upon, a greater desire to control whether and when they conceived and delay further pregnancies. At different times in their lives, both social norms and reproductive agency, specifically 'distributed agency' played significant roles in influencing their reproductive decision-making. Social norms held the most influence when they were teenagers and experiencing normative pressures to have a baby while young. As they grew older and/or had a first child they began to assert some agentic control around their reproduction. We therefore recommend that in order to improve the effectiveness of services and interventions supporting young women to delay unplanned pregnancies, programmers, researchers and policy makers must develop a better understanding of the role of social norms and agency at different stages of women's lives.