Systems and methods for calculating and predicting performance characteristics, incremental heat rate, capacity, incremental costs, production cost and emissions, for electric power generation plants, and in particular, those that use steam and gas-turbine prime movers. The system includes models and modules for calculating current unit performance and predicting unit performance, including the incremental heat rate and maximum capacity, using unit operating parameters, unit configuration data, and fuel constituency data. The system further includes a module for forecasting or predicting unit performance and cost information, by allowing the user to alter unit configuration and fuel constituency data to model planned maintenance and projected fuel changes, and to account for anticipated atmospheric conditions.