Purpose: Calculus is generally offered as a freshman year course and is a prerequisite for some advanced STEM-related courses in some undergraduate programs. However, some students experience difficulties in Calculus courses, leading to lower levels of achievement. Thus, there is a need to examine the factors which may be related to students' achievement in Calculus courses. According to relevant literature, procrastination can diminish students' achievement. Additionally, flow emerges as an important factor that may be related to students' achievement and procrastination, but these relationships have not been studied in the context of Calculus courses. The purpose of this study was twofold. Firstly, undergraduate students' academic procrastination was examined in relation to dimensions of flow experiences in a Calculus-I course. Secondly, undergraduate students' academic achievement in Calculus-I course was explored in relation to their academic procrastination and dimensions of flow experiences. Research Methods: A total of 117 undergraduate students (54% female and 46% male, M[subscript age]=23.00) from various departments participated in an online survey. Findings: Multiple regression analysis showed that among flow-experience dimensions, "concentration on the task at hand" was negatively related to procrastination. In addition, two-step hierarchical regression analysis indicated that procrastination negatively predicted achievement in the first step. However, in the second step, only the "challenge-skills balance" dimension of flow positively predicted achievement. Implications for Research and Practice: In Calculus courses, if students are given tasks that foster their focus, their procrastination behavior can be diminished. In addition, if they are given tasks that are appropriate to their level and skills, their academic achievement can be predictably higher. In this context, real-life applications should relate to students' own interests and skills. Therefore, their academic achievement can be higher.