Should fundraisers ask a banker to donate “if he earns a bonus” or wait and ask after the bonus is known? Standard EU theory predicts that these approaches are equivalent; loss-aversion and signaling models predict a larger commitment before the bonus is known; theories of affect predict the reverse. In five experiments incorporating lab and field elements (N=1363), we solicited charitable donations from small lottery winnings, varying the conditionality of donations between participants. Pooling across experiments, participants are 23% more likely to commit to donate from the winning income and commit 25% more when asked before the lottery’s outcome is determined—relative to those asked to donate after they learn they have won. These differences are strongly statistically significant. This represents the first evidence on how pro-social behavior extends to conditional commitments over uncertain income, with implications for charitable fundraising, giving pledges, and experimental methodology.