Finishing on time: When do predictions influence completion times?

People typically predict they will finish projects earlier than they do. Whereas previous research has examined the determinants of this prediction bias, the present research explored potential consequences for behavior. In particular, we examined whether and when task completion predictions influence actual completion times. In four experiments we used anchoring manipulations to induce participants to make relatively early or late task completion predictions, and then examined when they started and/or finished the target tasks. As hypothesized, the prediction manipulation influenced completion times under certain conditions defined by the nature of the target task. Manipulated predictions affected completion times of closed tasks, defined as tasks carried out within a single, continuous session but not of open tasks, defined as tasks requiring multiple work sessions. This implies that task completion predictions help to initiate action, but their impact diminishes over the course of extensive, multi-stage projects.