Consumers prefer products that deliver benefits for a longer time. For instance, caffeinated drinks are consumed for energy, but the key characteristic that performs this benefit—caffeine—tends to wear off in its effects. How can marketers communicate the lasting performance of product characteristics? This work proposes that numbers used in conveying product characteristics—round (200 mg) or precise (203 mg)—influence consumers' perception of lasting performance and product attitudes. More specifically, product characteristics described in round (vs. precise) numbers are perceived as performing for a longer time, and this effect is driven by a symbolic association between round numbers and stability. This finding is important because numbers are commonly used in conveying product benefits and past work has mainly documented the advantages of using precise numbers (e.g., higher competence), whereas less is known about when and why using round numbers boosts product attitudes. Three studies, including one with actual consumption, offer triangulating evidence for this prediction and its underlying psychological mechanism. Overall, this work contributes to research on product perception, numerical cognition, and persuasion.