Purpose <p> Counterfactual thinking about how past events might have been different, and prefactual thinking about how things might be different in future, contribute to judgements, emotions and decisions, and can impact mood and wellbeing. We present a new objective psychometric measure, the Counterfactual and Prefactual thinking Scale (CAPS). The CAPS allows for the measurement of counterfactual and prefactual thinking tendency in terms of perceived controllability and the direction of outcome (upward thoughts of how things might be better and downward thoughts about how things might be worse).</p> Methods <p>In Study 1, we present the development of the CAPS. In Study 2, particpants (general public <i>n</i> = 200; students <i>n</i> = 182) completed the CAPS as part of an online survey to demonstrate its validity and reliability against established measures of emotions and coping.</p> Results <p>CAPS subscale scores explained variance in three well-documented correlates of counterfactual thinking, regret, depression and anxiety symptoms, and also in hope. Our counterfactual and prefactual subscales are associated with different emotions consistent with existing literature. Upward counterfactual thoughts are associated with negative moods whereas upward prefactuals are linked to positive moods. The reverse occurs for downward thoughts and the CAPS captures this pattern.</p> Conclusions <p>The CAPS presents a new way to assess the tendency to counterfactual and prefactual thoughts. These may contribute to coping through mood regulation. The CAPS has potential utility in addressing applied and theoretical research questions.</p>