Regular physical activity is an important health promoting behavior. Yet, many adults live sedentary lifestyles, especially during their workday. The current study applies an extended theory of planned behavior model, incorporating affective attitudes and instrumental attitudes, along with habit, to predict limiting sedentary behavior and physical activity within an office environment. Theory of planned behavior constructs and habit were assessed with an online survey on a sample of 180 full-time office workers, with self-reported behavior assessed 1 week later (Mage = 25.97, SDage = 10.24; 44 males, 134 females, and 2 nonbinary). Model fit was indicated by BRMSEA (M = 0.057, SD = 0.023), B γ^ (M = 0.984, SD = 0.010) and BCFI (M = 0.959, SD = 0.026), accounting for 46.1% of variance in intention, 21.6% of variance in sedentary behavior, and 17.4% of variance in physical activity behavior. A Bayesian structural equation model revealed direct effects of instrumental attitudes and perceived behavioral control on intention to limit sedentary behavior, direct effects of intention and perceived behavioral control on limiting sedentary behavior, and direct effects of perceived