The ability to project oneself into the future has previously been found to be related to happiness and anxiety. The purpose of the present study was to investigate the causal effect of deliberate mental time travel (MTT) on happiness and anxiety. More specifically, we address whether purposely engaging in positive, negative, or neutral future MTT would lead to different levels of happiness and anxiety. Results show a significant increase of happiness for subjects in the positive condition after 2 weeks but no changes in the negative or neutral condition. Additionally, while positive or negative MTT had no effect on anxiety, engaging in neutral MTT seems to significantly reduce stress over 15 days. These findings suggest that positive future MTT is not just a consequence of happiness and might be related to well-being in a causal fashion and provide a new approach in happiness boosting and stress-reducing activities.