Within our increasingly technological society, there is widespread acknowledgement of the need to build student participation in school STEM subjects. Within the current ‘STEM agenda’, the Australian government is specifically targeting calculus-based mathematics participation and the engagement of students from underrepresented equity groups, including girls. Recent research in this area indicates that one of the most important factors influencing student enrolment in calculus-based mathematics is perceived need of the subject for future careers or study. Understanding students’ aspirations for careers that require a high level secondary mathematics background, may therefore be integral to understanding girls’ underrepresentation in mathematics. However, there is a lack of current research that directly links career aspirations and secondary mathematics requirements. In order to understand this link we compiled statements of assumed knowledge (level of mathematics) for particular courses of study from university entrance guides. We also used survey data from more than 6,000 students in Years 3 to 12 and interviews with 38 female students with high to mid prior mathematics achievement. Our analysis of these data revealed that girls were slightly less likely to aspire to a career requiring calculus-based mathematics than boys. However, strong gender differences emerged when these careers were separated into core (advanced calculus) and related (entry-level calculus) categories. More than 30% of the boys who named a career requiring high-level mathematics named a career requiring advanced calculus, compared with only 4 % of girls. Core aspiring boys, compared to non-core aspiring boys, were generally from more advantaged backgrounds with higher achievement levels. However, as a group, the core aspiring girls were even more advantaged and had even higher levels of achievement than the core aspiring boys. Our analysis of interview data revealed that many girls excluded themselves from considering careers requiring calculus because they saw such careers as being for those with ‘natural’ mathematics ability, or for boys. The few girls who expressed an affinity for mathematics careers expressed concern about the sexist environments they might enter, to the extent that it impeded their aspirations and only the brightest and most advantaged girls were able to maintain such aspirations. Given these results, we argue that unless stereotypes, and the culture of male-dominated fields, change to be welcoming for more diverse individuals then we are not likely to see any change in the number of girls aspiring to these professions and, relatedly, studying high level mathematics during secondary school.