According to a long tradition of research, people are used to mentally time travel: That is, to recreate memories from the past and envision future scenarios. To date, a growing body of evidence has revealed that people’s estimations about past and future emotional states are inaccurate. Nevertheless, the mechanisms underlying these biases are still understudied, and the potential role of response style to positive affect (PA) has not been explored yet. Here, we implemented a two-week Ecological Momentary Assessment (EMA) design to monitor PA in 84 healthy individuals, who were asked to forecast and recall their mood before and at the end of the study. According to the results, participants with high levels of emotion-focused positive rumination showed higher accuracy in forecasting future PA, whereas participants with high self-focused positive rumination overestimated future PA and were highly accurate in retrospectively recalling experienced PA. Altogether, we suggest that more accurate or positively biased estimations of past and future states may in part be the consequence of an individual’s predisposition to ruminate on positive experiences and self-qualities