Self-Directed Informal Digital Learning of English (SD-IDLE) plays a crucial role in informal language learning. This study aims to examine the SD-IDLE nature of English learning among Indonesian university students and its impact on language learning and personal development. The research used a sequential explanatory mixed methods design, employing a questionnaire and semi-structured interviews as research tools. Data were collected from 302 Indonesian university students enrolled in various EFL classes at three universities. The study revealed that the nature of SD-IDLE activities was significantly associated with the English proficiency of EFL students, although the results for each component varied. The nature of self-management and monitoring activities showed a significant positive correlation with students' English proficiency, while the nature of self-motivation activities displayed a negative correlation. In conclusion, students who actively engaged in the nature of SD-IDLE activities such as good goal commitment, resource needs, metacognition, and broad social communication needs demonstrated higher English proficiency. However, students who relied solely on motivation did not consistently achieve successful English proficiency scores.