Our study seeks to contribute to scholarly understanding of the antecedents and consequences of the crucial, but so far overlooked within-person daily fluctuations in presenteeism. Drawing on theoretical frameworks of presenteeism, which conceptualize presenteeism as an adaptive behavior to deliver work performance despite limitations due to ill-health, we develop a within-person model of daily presenteeism and examine somatic complaints and work-goal progress as crucial joint determinants of daily fluctuations in presenteeism. We further integrate the aforementioned theoretical frameworks with ego-depletion theory to argue that presenteeism requires self-regulation to suppress cognitions, emotions, and behavioral responses associated with ill-health and instead focus on completing one's work tasks. Accordingly, we predict that presenteeism depletes employees' regulatory resources and impairs employees' next-day work engagement and task performance. The results of a daily-diary study across 15 workdays with N = 995 daily observations nested in N = 126 employees show that daily work-goal progress attenuates the daily relation between somatic complaints and presenteeism, thereby also reducing the indirect effect of somatic complaints on employees' next-day work engagement and task performance through presenteeism and ego depletion. We discuss the theoretical and practical implications of shifting presenteeism research from the macro- to the micro-level. (PsycInfo Database Record (c) 2022 APA, all rights reserved).