This paper presents an agent-based model for decision making, which integrates personal biological and psychological aspects with rational utility-based reasoning. The model takes a BDI-based approach, where generation of desires is based on the personal characteristics, and generation of intentions is based on the rational reasoning. Moreover, a hypothetical reasoning mechanism is exploited to derive knowledge that connects certain actions to desires. The model has been implemented in the LEADSTO environment, and has been applied in a case study in the domain of criminal behaviour. Simulation experiments pointed out that the model enables agents to reason effectively about the consequences of their actions, which helps them to make the decisions that best satisfy their desires.