We investigate the impact of rebates and refunds on contributions to threshold public goods using evidence from a field experiment conducted in conjunction with an Australian charity, Life Goes On. We find that offering rebates and refunds has a significant positive impact on both participation and average donations in the absence of seed money. Our results suggest that offering rebates and refunds, and the existence of seed money may, to some extent, play substitute roles in encouraging giving behavior. Seed money has a significant positive effect on participation only. Seed money's impact on average donations may be mitigated by a threshold effect.