Do time constraints impact charitable giving? This paper develops a simple model to show how deadlines could affect the propensity to make a charitable donation. We then conduct two field experiments to show empirically the effect of deadlines on charitable giving. About 53,000 prior donors of a large Danish charity received e-mails and text messages with varying deadlines for giving. We find no effect of deadlines on the propensity to give. Instead we observe a “now-or-never” effect; either donations are made immediately or not at all.