This paper uses a multi-wave experiment to test the effects of time-limited, multi-organization giving days, such as Giving Tuesday, on later donations to nonprofit organizations. Although Giving Tuesday raised $274 million in 2017, some organizations fear the day displaces, rather than increases, year-end giving. This paper uses a multi-wave online survey experiment to simulate end-of-year giving conditions. We determine how a randomized multi-organization solicitation treatment affects giving to later solicitations, which are each spaced approximately one week apart and targeted to respondent preferences. The survey design highlights differences across sector as well as respondents’ stated organization familiarity, giving history, and charitable preferences. In addition to advancing theory on how solicitations lift and shift charitable giving, this work helps nonprofit organizations to better gauge the costs and benefits of participation in giving days and in other year-end appeals.