Adults hold optimistic beliefs for online behaviours, displaying a general tendency to believe that they are less likely to experience general risks than others. Study 1 explored whether young adults displayed comparative optimism judgements for four types of specific risks that were relevant to a UK sample. Study 2 addressed methodological weaknesses associated with assessing comparative optimism. Study 1 explored 227 (194 female, 31 male, 1 non-binary, and 1 gender not disclosed) young adults’ (MAge = 20.75, SDAge = 4.22) comparative optimistic beliefs for unwanted contact, hoaxes, behavioural, and sexual online risks that were contextualised to the UK. In study 2, young adults (134 female, 30 male, 1 non-binary, and 1 gender fluid, MAge = 20.72, SDAge = 3.39) provided judgements for four online risks for the general public and the comparator groups used in study 1. Participants were then provided with the prevalence rate for each risk according to data for the UK and then asked to repeat the judgments for each comparator group. Study 1 identified optimistic beliefs across the four risks, with family and the self judged to be less at risk. Study 2 revealed that again family was perceived to be at the lowest risk followed by the self. Knowledge of the actual risk led to a reduction in perceived risk for unwanted contact and hoaxes but little change for behavioural or sexual risks. Together, the findings have implications for understanding perceptions of online risk and how campaigns to promote digital safety are designed.