Previous studies explain loss aversion as the result of a situation in which the expected negative emotions derived from a potential loss exceed the expected positive emotions derived from a potential gain (subtractive logic). We questioned this view and proposed additive logic, in which a linear combination between negative and positive emotions can be used as summed anticipatory affect intensity (SAAI) to explain loss aversion. By disproving two implicit hypotheses of subtractive logic, Study 1 showed that the additive logic of expected positive and negative affect was more effective than the subtractive logic in predicting loss aversion. Study 2 used real monetary gains and losses to verify the conclusion in Study 1. Using state‐trait theory to comprehensively consider the state and trait aspects of affect intensity, we further deduced that the immediate expected affect intensity might originate from the difference of an individual trait in affect intensity. Study 3 proved this hypothesis and showed that SAAI plays an intermediary role between affect intensity and loss aversion. Furthermore, Study 4 used real gamblers in casinos in Macau as its sample and obtained the same conclusion regarding loss aversion in real life as was found in the laboratory. Finally, we explained the effect of SAAI on loss aversion and indicated the contribution and significance of this study. Copyright © 2015 John Wiley & Sons, Ltd.