Declining interests in STEM (science, technology, engineering, and mathematics) related careers are concerning at a time when the society is becoming more reliant on complex technologies and science. Our study examined the predictors of students' STEM career interests within cohort data (N = 601) collected from Finnish general upper secondary schools. We created a SEM research model based on the Social Cognitive Career Theory, to explore how (1) Career outcome expectations, (2) Natural science subject interests, (3) Mathematics self-efficacy beliefs, (4) Receiving career information from various sources, (5) Support for mathematics studies related to (6) students' STEM career interests. A structural equation modelling (SEM) analysis showed receiving career information from various sources had a positive effect on STEM career interest. Likewise, mathematics self-efficacy beliefs positively related to natural science subject interest which, in turn, contributed to students' interest towards STEM careers.