This paper tests the predictive value of subjective labour supply data for adjustments in working hours over time. The idea is that if subjective labour supply data help to predict next year’s working hours, such data must contain at least some information on individual labour supply preferences. This informational content can be crucial to identify models of labour supply. Furthermore, it can be crucial to investigate the need for, or, alternatively, the support for laws and collective agreements on working hours flexibility. In this paper I apply dynamic panel data models that allow for measurement error. I find evidence for the predictive power of subjective labour supply data concerning desired working hours in the German Socio- Economic Panel 1988-1996.