Self-efficacy is strongly correlated with academic success, persistence within a major, and career choice. Calculus courses have been shown to be a weak point in the STEM pipeline, where attrition after completing a calculus course is higher than any other factor or time point. The purpose of this study is to examine how academic and interpersonal experiences within a large calculus course impact mathematical self-efficacy. Furthermore, this study aims to determine whether differences in mathematical self-efficacy are impacted by the identity factors of gender, race, or major. This study employed a mixed-method approach with triangulation design. Analyses revealed significant differences in mathematical self-efficacy between identity subgroups at the beginning of the course, and perpetuated differences by the end of the course supporting prior research showing that women and URM students tend to leave STEM at higher rates. Interviews and qualitative data illuminate why these trends may have occurred.