<p>Ageism refers to stereotypes, prejudice, and discrimination based on age. Ageism negatively impacts physical and mental health across the lifespan, yet knowledge about the experience of ageism in Singapore is limited. This study evaluated the prevalence of experienced ageism in Singapore and identified its key determinants within a nationally representative cohort. In the cross-sectional HEalthy LOngevity (HELO) survey (<i>N</i> = 3034), ageism was measured using the newly launched World Health Organization (WHO) Ageism Experiences Scale. Associations with chronological age, perceived age, gender, socioeconomic, and health-related factors were examined using nonparametric tests and multivariable linear regression. Respondents’ median chronological age was 46 [interquartile range (IQR): 34–59] years, and 54.1% were female. Experiences of ageism were reported by 49.4% of respondents. Total ageism scores were on average 1.5 points higher among the youngest (21–30 years) and oldest (71+ years) age groups and approximately 1 point higher among respondents with lower socioeconomic status, particularly those with lower education levels. Respondents who felt older than their chronological age reported significantly higher ageism scores. This first large-scale study on ageism in Singapore reveals high experienced ageism, consistent with global estimates, particularly among older and younger adults. Feeling older was one of the strongest ageism predictors. Addressing ageism by targeting social determinants and subjective ageing perceptions is essential to promote healthy ageing and to inform public health policy and interventions in Singapore.</p> Graphical Abstract <p></p>