This study examines the determinants of underemployment among part-time employed Australian females, accounting for the interaction of their age, educational qualifications and offspring presence. Females who are young, tertiary educated and without offspring are likeliest to be underemployed, and in general the presence of children lowers the probability of underemployment for those aged below 35, but this impact ameliorates significantly for those aged 35 and above. Policies to address female underemployment need to account for the fact that there is no representative ‘average female worker’, so as to ensure requisite policies better target those most at risk of underemployment. This finding holds for those working either minimum or maximum hours within the part-time spectrum, where greater uniformity of underemployment is found. Age of offspring affects the likelihood of underemployment with younger offspring reducing the incidence of a mismatch between preferred and actual hours, while the opposite holds for older offspring.