Time scarcity promotions (e.g., “40% off for a limited time”) are mainstays of retail marketing. But might translating them to online shopping contexts alter or nullify their efficacy? The authors first report a meta-analysis of published and unpublished research as well as a simulated shopping experiment suggesting that the positive effects of time scarcity promotions observed offline may not emerge in online shopping contexts. They then posit that this difference arises because, in the online context, time scarcity promotions activate persuasion knowledge, which in turn changes their effects. In support of this, the authors demonstrate that when retailer-exogeneous justifications are given for online time scarcity promotions (e.g., consumers’ birthdays, seasonal changes), persuasion knowledge activation is decreased, improving time scarcity promotions’ effects on consumer interest. Further, when an exogenous justification is combined with less, as opposed to more, time until an online promotion’s expiration, significant positive effects on consumer engagement may be observed. However, effects stop short of suggesting that time scarcity promotions will consistently yield superior outcomes compared to identical control promotions online. Therefore, the authors highlight the continued need for careful managerial use as well as further research related to the optimal translation of offline tactics to online retail.