Non-profit organisations have a strong interest in understanding how best to motivate volunteer effort. In fundraising settings, getting volunteers to set themselves fundraising goals is a common approach but little is known about the effect of goal-setting in this context. We present findings from a large-scale field experiment run by a major online fundraising platform used by individual (i.e. non-professional) fundraisers to raise money for charity. The treatment – a default target value (the value of which varied randomly) – was designed to increase goal-setting. The experimental set up allows us to look at both default effects, i.e. the effect of the defaults on goal-setting, and goal effects, i.e. the causal effect of goal-setting on fundraising outcomes. Overall, we find no effect of goal-setting on fundraising outcomes (how much money is raised) but this masks different (significant) effects for men and women. Briefly summarizing the main findings: First, we find that men are more ambitious insetting goals than women. In the control group, men are more likely than women to set a goal and set higher-value targets. The effect of the defaults is to reduce the goal-setting (0/1) gender-gap, but not the gender gap in goal values; women set lower targets, even conditional on past performance. Second, we find a stronger positive goal-value effect for men than for women. Men’s fundraising performance responds positively to high goals and negatively to low goals (compared to no goals). By contrast, women’s fundraising performance is only improved (compared to no goal) by low goals. Using a simple model, we discuss what our results imply about goal-setting behaviour by men and women.