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This paper presents a mathematical model to determine the minimum energy targets for a batch process with flexible schedule. Techniques developed for flexible-schedule batch processes typically result in nonlinear formulations. The proposed model was formulated as a mixed integer linear programming model (MILP). The model is developed based on the source-demand classification of process streams instead of the typical classification of hot and cold streams. In such classification, each stream is simultaneously treated as a source at its shifted supply temperature, and as a demand at its shifted target temperature. Such classification eliminates the model's non-linearity and reduces its complexity as well as the solution time. The mathematical model can be used to calculate the utility targets for a flexible-schedule batch process. Application of the proposed mathematical formulation demonstrates significant energy saving potential. The first illustrative example predicted a potential reduction of 11% cold utility and 14% hot utility. In the second illustrative example, up to 35% hot utility reduction and 62% cold utility reduction could be achieved. [ABSTRACT FROM AUTHOR]