This study examined gender differences in reading behavior of 2652 Danish 5th-grade students (age 10-12 years, girls 51%, 14% immigrant background) observed for 218 days in 2019/2020, using data from a popular reading app. Reading behavior was operationalized as time spent reading. Analyses of timing of reading behavior and models of day-to-day reading time were employed to investigate the gender gap in reading behavior. Results show that girls read more than boys. This differential can be attributed to girls reading more outside school hours, during weekends and holidays than boys while there are no gender differences in reading activity during school hours. Results suggest that girls with positive academic attitudes were more inclined to read than boys with similar attitudes.