Whether and how people regulate their negative emotions matters a great deal. However, it is not yet clear why people regulate as they do. One promising idea is that people's beliefs shape their emotion regulation choices, and initial evidence indicates that individuals' dispositional beliefs about emotions are indeed associated with general patterns of emotion regulation. The present study extends prior work on emotion beliefs to better understand how occurrent (i.e., momentary) beliefs about helpfulness, controllability, and justification of specific emotions shape whether and how people regulate negative emotions in everyday life. Participants (N = 143; U.S. community college students recruited in 2022; 76% female; age = 18-60) completed a 7-day experience-sampling protocol in which they were pinged three times per day to describe their most recent negative experiences and answer questions about their emotions, occurrent beliefs about emotions, and emotion regulation. With respect to whether people regulate their emotions, results reveal that people regulate their emotions more when they perceive them to be less helpful. Exploratory analyses additionally show that people regulate negative emotions more when they perceive them to be more controllable and when emotional intensity is relatively high. In terms of how people regulate their emotions, people are more likely to use reappraisal when emotions are seen as more helpful, more controllable, and less justified; and more likely to use distraction when emotions are seen as less helpful and more justified. These findings contribute to a more fine-grained understanding of how beliefs shape emotion regulation in everyday life.