The study analyses the relationship between formal and informal telework and work-family conflicts using the job-demands and resources (JD-R) model. Previously, the model has more frequently been applied to understand the implications of telework without distinguishing between formal telework and informal telework outside contracted working hours. We conducted cross-sectional OLS-regressions on pilot data from the European Social Survey compiled in 2019. The results show that formal telework is associated with fewer, and informal telework with more work-family conflicts. While formal telework appears as a resource, informal telework rather functions as a demand. Additional analyses report that formal teleworkers are nevertheless at risk of work-family conflicts because formal telework often goes hand in hand with informal telework and, thus, work-family conflicts.Practical Relevance: While formal telework can facilitate the reconciliation of work and family life, employees are at risk of counteracting this dynamic when telework is conducted informally during paid or unpaid overtime. The findings suggest that it is important for managers, HR managers and employees to be aware of the potentials and risks of frequent teleworking that come with the ability to work anytime and anywhere in order to avoid unintended consequences. In this context, an organisational culture that values adherence to schedules and ‘switching off’ at the end of the workday, even under conditions of high workloads and low personnel resources, can be beneficial.