This research investigates how provision of calories-per-serving information on serving size labels affects snack consumption quantity. Drawing from expectancy-disconfirmation theory, this research shows that providing calories-per-serving information can ironically create a consumption backfire effect (consumers eat more when presented with calories-per-serving information) for snacks perceived as unhealthy but not for snacks perceived as healthy. The authors find that this effect arises when calorie expectations are higher than the posted calories-per-serving level—a frequent occurrence due to stated serving sizes that are typically smaller than amounts consumed in one sitting. The authors also show that attention to calorie information plays a key role such that the backfire effect occurs among consumers who pay more attention to calorie information. Furthermore, motivational factors including individual differences and perceptions of the risk associated with consuming a snack also play a role in driving consumption differences. The authors offer managerial, policy, and consumer welfare implications, including proposing and testing larger stated serving sizes as an intervention.