Employees who remain available for work outside regular work hours often experience strain and work–home conflicts. This study clusters employees in distinct availability types based on different aspects of unregulated extended work ability, which are contacting frequency, availability expectations and perceived legitimacy of availability. Moreover, we examined covariates of class membership and relationships with employees’ well-being. We used data from 17,410 employees who took part in a representative survey of the German working population. Latent class analysis with double cross-validation revealed three availability types. Satisfaction with work–life balance was higher and internal work–home interference was lower in the “rarely available”-class than in the “legitimate available”-class and the “illegitimate available”-class. Members of the “illegitimate available”-class reported worse subjective health, more psychovegetative health complaints, and higher levels of exhaustion than members of the “legitimate available”-class and the “rarely available”-class. Several socio-demographic variables, job characteristics, and factors associated with boundary management predicted class membership. Overall, the study highlights the risks for employees’ well-being associated with unregulated extended work availability – particularly when it is perceived as illegitimate – and points towards implications on the individual, organisational, and political level that may help reduce and better manage extended work ability.