Subjective age discordance (SAD) captures the difference between how old one feels and how old one would ideally like to be. We investigated the presence, strength, and fluctuation of this discordance in daily life as well as its relationship to various indicators of physical and psychological well-being with an 8-day diary study. Participants were 116 older and 107 younger adults who completed daily measures of felt age, ideal age, positive and negative affect, physical symptoms, and stressors. We operationalized SAD as felt age minus ideal age divided by chronological age and compared the utility of this discordance to the more established proportional discrepancy of felt age from chronological age. Daily SAD was present in both age groups, such that individuals idealized younger ages than they felt. This discordance was larger in older than younger adults, although younger adults exhibited more daily fluctuations in SAD. Within-person increases in SAD were associated with lower positive affect, whereas larger SAD at the between-person level was associated with more physical symptoms and stressors. These relationships were over and above the associations of felt and chronological age with the outcomes suggesting the utility of daily SAD for understanding daily physical and psychological well-being. (PsycInfo Database Record (c) 2021 APA, all rights reserved).