Recent research has found that the menstrual cycle affects product preferences. However, might the menstrual cycle also impact whom women prefer to spend their money on? Drawing from evolutionary theory, we predict and find that women are more prosocial during the luteal phase than during the follicular phase. Across three studies, we show that women allocate more money towards gifts for loved ones during the luteal phase, and that this prosociality extends to anonymous others through charitable donations and via an established social orientation task. Furthermore, we find that the menstrual cycle effect on prosociality is mediated by perceived dependence on others. Taken together, our findings suggest that the luteal phase not only prepares women's bodies for a potential pregnancy, but also prepares them psychologically by motivating them to depend on and foster social alliances that historically would have been beneficial in the event of a pregnancy.