We provide new large‐scale experimental evidence on policies that aim to boost household saving out of income tax refunds. Households that filed income tax returns with an online tax preparer and chose to receive their refund electronically were randomized into eight treatment groups, which received different combinations of motivational saving prompts and suggested shares of the refund to save—25% and 75%—and a control group, which received neither. In treatment conditions where they were presented, motivational prompts focused on various savings goals: general, retirement, or emergency. Analysis reveals that higher suggested that allocations generated increased allocations of the refund to savings but that prompts for different reasons to save did not. These interventions, which draw on lessons from behavioral economics, represent potentially low‐cost, scalable tools for policy makers interested in helping low‐ and moderate‐income households build savings.