Extensive reading (ER) is widely recognized for improving language proficiency, but its impact on reading comprehension over time is less understood. This study investigates how Xreading, an online ER platform, influences students’ reading comprehension over two semesters in the Miyazaki Municipal University English Language Program. Using pre- and post-test scores from the Edinburgh Project on Extensive Reading (EPER), results show that students make significant gains at the end of the first semester compared to the beginning. However, improvement is less pronounced at the end of the second semester. These findings suggest that while ER enhances comprehension, the rapid gains in the first semester may reflect an initial learning curve, with progress slowing as students reach a plateau in the second semester. This presentation will discuss the implications for ER integration in academic programs and strategies to maximize its long-term benefits.