The present invention relates to a mental balance or imbalance estimation system (100) and method for estimating a level of mental balance or imbalance of a user (1). The system comprises a skin conductance sensor (20) for sensing the skin conductance of the user (1), the skin conductance over time forming a skin conductance trace (22). The system further comprises a processing unit (10) for receiving and processing the skin conductance trace (22), the processing unit configured to determine at least one stimulus response (24) in the skin conductance trace (22), to determine an estimated cortisol level trace (28) of the user (1) based on the determined at least one stimulus response (24), and to determine the estimated level of mental balance or imbalance of the user (1) based on the estimated cortisol level trace (28).