A method and system for determining the overall performance of a power plant are provided. The system includes a plurality of components including a processor configured to generate a first reference model of the power plant and generate a first measured model of the power plant. The processor is further configured to determine the performance impact of the at least one of the plurality of components of the power plant on the overall thermal performance of the power plant, normalize the performance impact to design conditions, and output at least one of the normalized performance impact on overall plant performance.