Objectives: Many sedentary individuals are aware of the health benefits of regular physical activity and start becoming more physically active. Yet, despite good intentions, many struggle to keep up initial exercise levels and experience a decline in exercise frequency. A possible explanation is that it is hard to establish habits or routines, and that such routines - once established - might be easy to break. In this paper, we analyse whether a break in habitual/routine behaviour - induced by the Easter holidays - results in individuals exercising less after the break. Methods: The study included a sample of 1210 members of a Danish chain of fitness centres who were gym members at least since the preceding New Year's Day. Participants granted access to gym attendance data, which were automatically recorded when entering the gym. We use a regression discontinuity design encompassing a time period of 10 weeks prior to and 10 weeks after Easter. Results: We found a significant and relevant discretionary drop in exercise frequency right after the Easter holidays of 0.24 times per week (p=0.001) corresponding to a fall of 12.25% compared with the week prior to the Easter holidays. The effect was especially profound for individuals below retirement age and for individuals who had attended the gym with a higher frequency (twice a week or more) in the 6 weeks prior to the Easter break. Discussion: This information is potentially relevant for helping individuals maintain an exercise habit. Motivational support should focus on the time period after normative breaks, such as Easter or other holidays.