Why do people work unpaid overtime? We show that remarkable long-term labor earnings gains are associated with unpaid overtime in West Germany. A descriptive analysis suggests that workers with unpaid overtime experience on average at least a 10 percentage points higher increase in real labor earnings over a 10-year period than their co-workers. Applying panel data models this result generally holds. Furthermore, we find evidence for gender specific earnings differentials with respect to cumulative average unpaid overtime work. Our results point to the importance of investment into current working hours beyond the standard work week to enhance real earnings prospects.