Life is full of mundane tasks such as commuting, attending meetings, and filing paperwork. Despite their ubiquity, experience with mundane tasks remains understudied in the literature. Across a series of lab and field studies, we show that the negative feelings about a mundane experience are impacted by people’s perception of how much of the task has been completed, which we term relative task completion. Contrary to people’s intuition, we find that the same ongoing task (e.g., sitting through a boring meeting for 20 min) feels less aversive when relative completion is lower (e.g., in a 60-min meeting) than when it is higher (e.g., in a 30-min meeting). Our studies suggest this may occur due to ratio sensitivity: People infer that they have endured less after completing a smaller, rather than a larger, proportion of a mundane task, which reduces negative feelings. Data also showed that people lack insight into the impact of relative task completion and ruled out alternative explanations including response scale anchoring, progress focus, and preparation while suggesting mood regulation and attention as parallel explanations in some contexts. Finally, we identify busyness as a moderator and develop three low-cost interventions to manipulate perceived relative task completion and improve mundane experiences. (PsycInfo Database Record (c) 2025 APA, all rights reserved)