Background <p>How would you rate your health today? Self-rated health is a key indicator of overall well-being, yet little is known about how daily fluctuations in self-perceptions of ageing relate to day-to-day variations in health. This study investigated whether daily fluctuations in subjective age and awareness of age-related change are associated with variations in self-rated health across adulthood.</p> Methods <p>For 10 consecutive days, participants (<i>N</i> = 78, age range 20 to 81) completed daily questionnaires, via the m-path application, assessing their daily subjective age, awareness of age-related gains and losses, and self-rated health. Multilevel models were used to examine associations at both the between- and within-person levels, as well as moderation by chronological age.</p> Results <p>Both average and daily subjective age were significant associated with self-rated health across the lifespan, such that feeling younger was related to better self-rated health. At the between-person level, higher awareness of age-related losses, but not gains, was associated with poorer self-rated health. In addition, chronological age moderated the associations between subjective age and self-rated health at both the between- and within-person levels. In particular, on days when they felt older than usual, younger participants reported worse self-rated health than older participants. challenging the notion that subjective age is only associated with outcomes in later life.</p> Conclusions <p>These findings highlight the importance of considering self-perceptions of ageing as dynamic processes that shape daily health evaluations across the adult lifespan, including early and mid-adulthood.</p>