Child marriage violates human rights and is a significant impediment to achieving the 2030 Agenda for Sustainable Development. Although progress has been made in reducing child marriage worldwide, it remains prevalent (including in the Arab region), fuelled by sociocultural norms, poverty, lack of education, and external factors such as conflict or natural disasters. Research confirms that child marriage has severe and far-reaching consequences for women and girls, affecting all aspects of their lives, families and society. This new study estimates the costs of child marriage at different stages of women’s lives, using a life-cycle skill formation model in four Arab countries, namely, Egypt, Iraq, Jordan, and Tunisia. The study provides new insights into the multifaceted costs of child marriage and highlights the urgent need for action to eliminate this harmful practice.