Mathematical proficiency is essential to supporting students' success in learning mathematics. It is the ability to use conceptual understanding, procedural fluency, strategic competence, adaptive reasoning, and productive disposition in problem-solving. Cognitive independence shows students' ability to process information. Meanwhile, motivation is related to things that encourage students to learn mathematics. This study aims to determine the effect of cognitive independence and motivation on mathematical proficiency. It involved 131 students and used a mixed method with Sequential Explanatory Design. The quantitative research part of the study was used to determine the effect of cognitive independence and motivation on mathematical proficiency using a multiple linear regression test. Furthermore, qualitative research was used to deeply scrutinize the effect by using in-depth interviews. The results showed that students with high cognitive independence could process the knowledge that has been possessed logically, while students with low cognitive independence did it illogically. Students with low motivation use trial and error strategies to maximize mathematical proficiency, while students with high motivation use analytical strategies.