Background: In the context of sedentary lifestyle as a major contemporary health issue, this study examined how an ultra brief exercise bout affects perceived subjective well-being. Material/Methods: Two studies were conducted. In the first study, young participants performed light exercises for 3-minutes. The second study replicated the first, but a sitting-quietly control group was also included to account for possible habituation or order effects. On a single item 10-point Likert scale, conceptualized as core affect, participants rated their well-being immediately before and after the exercise bouts and rest, respectively. Results: In both studies the exercise triggered statistically significant (p < .001) improvement in the perceived well-being (effect sizes (d) = .62 in Study I, and d = .75 in Study II), while no statistically significant change was noted in the control group. Conclusions: These findings are the first ever in the scholastic literature to demonstrate that only 3 minutes of light exercises could trigger subjective experience of improved well-being. The practical implication of these findings is that an instant boost in subjective feeling states can be achieved through very short, light, and undemanding exercises that could be repeated several times a day in different life settings.