In this paper a computational model is presented that describes the role of emotion regulation to reduce the influences of negative events on mood. Emotion regulation is a process based on a set of regulatory strategies used by persons to down-regulate their negative emotions or to up-regulate their positive emotions. For a given situation, the selection of specific regulation strategies is dependent on that particular situation. The current paper presents work focusing on a cognitive reappraisal (re-interpretation) strategy, that involves changing the way one interprets a stimulus or situation, or alter the semantic representation of an emotional stimulus in order to reduce the influence of such stimuli. The model incorporates an earlier model of mood dynamics and a model for the dynamics of emotion generation and regulation. Example model simulations are described that illustrate how adequately emotion regulation skills can avoid or delay development of a depression. The presented computational analysis shows how regulation of stressful emotions helps unstable persons to avoid a depression, and to postpone it in very unstable persons. Furthermore, the analysis shows that if a stressful event persists for a longer time period, then emotion regulation can also help an unstable person to prevent the mood level from becoming too low, for a certain time.