In this study, we consider the dynamics of crowdfunding project support over time. We propose that people support crowdfunding projects financially when they believe that their contribution will make an impact. Because perceptions of impact are positively related to goal proximity, we predict that support for a crowdfunding project will increase as the project funding approaches its target goal. In addition, because motivation decreases after a goal is attained, we further predict that crowdfunding contributions will significantly decrease after the target goal is reached. We find strong support for these hypotheses from a large-scale field study involving Kickstarter. Furthermore, we show that several factors related to the expected impact moderate the effects of goal proximity; that is, the positive effect of goal proximity on project support is accentuated if the project is nearing its funding deadline, if the target goal is relatively small, or if the project has limited early support.