A procedure for calculating appropriate loss coefficients and flow distribution parameters to initialize boiling water reactor (BWR) system transient codes is presented. This method achieves a pressure and flow balance while satisfying the constraint that the calculated steady-state flows and pressure drops match the plant performance curves supplied by the user. The methodology has been encoded in the REBAL computer code, which greatly reduces the engineering man hours required to achieve a properly initialized model. This methodology improves the accuracy and consistency of transient calculations performed at off nominal power and flow conditions and is particularly useful at the high-power/low-flow conditions typical of BWR stability analysis.