This study explores how foreign language enjoyment (FLE), foreign language classroom anxiety (FLCA), and L2 grit influence reading achievement in extensive reading (ER) programs. Underpinned by theories of Positive Psychology, the study investigates how these affective and personality factors impact reading amount, reading fluency, and reading comprehension. The study involved 49 university EFL learners who completed a questionnaire and participated in a six-week ER program on Xreading.com. The findings suggest that FLCA predicted reading amount, while FLE predicted reading fluency. However, FLE, FLCA, and grit did not significantly affect reading comprehension. The study provides valuable insights into the relationship between affective factors and reading achievement and offers theoretical and practical implications for ER teaching and research.