This study focuses on the problem that the process of building learning habits has not been clearly described. Therefore, we aim to extract the stages of learning habits from log data. We propose a data model to extract stages of learning habits based on the transtheoretical model and apply the model to the learning logs of self-directed extensive reading to demonstrate the process of building learning habits. We uncover the various stages (i.e., the precontemplation, contemplation, preparation, action, and maintenance stage) that learners underwent, and different proportions of the maximum stage that they achieved during an 11-month, self-directed, extensive reading program-implemented in a Japanese junior high school. This study contributes to realizing a method to evaluate the learning process, by tracing the stages of learning habits in long-term, and continuous learning activities. Further, this study can help guide the development of evidence-based educational interventions to support the building of lifelong learning habits and self-directed learning, using data-driven methods.