Despite the wealth of accumulated research evaluating subjective wellbeing (SWB) in children and adults, the validity of scores from parallel forms of SWB measures for each age group has yet to be empirically tested. This study examines the psychometric equivalence of the child and adult forms of the personal wellbeing index (PWI) using multiple-group confirmatory factor analysis. The child sample comprised 1,029 Victorian high-school students (aged 11-20) sampled across three independent studies. The adult sample comprised 1,965 Australian adults drawn from the Australian Unity Wellbeing Index. The results demonstrated strict factorial invariance between both versions, suggesting that the PWI measures the same underlying construct in adolescent and adult populations. These findings provide support for quantitative comparisons between adult and adolescent SWB data as valid.