A simple real-time model of the loss-of-fluid test (LOFT) reactor is derived and used to predict reactor performance during an anticipated transient without scram (ATWS). The developed model consists of only six nonlinear differential equations. Model states are precursor concentrations of two delayed neutron groups, average fuel and cladding temperatures, average core coolant temperature, and measured reactor outlet temperature. Ancillary dynamic descriptions of a hot fuel rod allow computation of peak rod temperatures. Comparing model calculations to actual LOFT ATWS measurements demonstrates the model’s phenomenological accuracy.