Day-of-week (DOW) effects such as "blue Monday," "Thank God it's Friday" (TGIF), and weekend effects have mostly been investigated using a cross-sectional approach with Western samples and focusing on hedonic aspects of well-being. Using large-scale data (N = 859,749) containing multiple observations per person collected from Koreans, we examined various patterns of DOW effects on comprehensive measures of well-being. Unlike previous studies, we examined DOW effects at the within-person level. Blue Monday and TGIF effects were evident across affective and evaluative/cognitive aspects of well-being, and the Thursday nadir phenomenon was also found. The DOW effects were consistent for the affective well-being, whereas no weekend effects were observed for the cognitive aspects, including life satisfaction and meaning in life. The DOW effects were moderated by gender and age groups, with younger people tending to experience more salient DOW effects and women identifying fewer benefits from DOW effects. (PsycInfo Database Record (c) 2021 APA, all rights reserved).