This paper describes a modified F-factor approach for real-time performance monitoring of heat rate and CO2 emissions for fossil fuel power plants. The calculation protocol introduced in the present investigation is a modification of the F-factor method mandated by the U.S. Environmental Protection Agency (EPA). It utilizes Continuous Emissions Monitoring Systems (CEMS) data to evaluate an F-factor based on actual conditions prevailing in the combustion process, and therefore is less reliant on the use of empirical correction factors. The proposed method is intended to be used in combination with a real-time output-loss performance monitoring approach described herein. It was shown that when modified F-factors were corrected back to standard conditions of stack pressure and temperature, and stoichiometric combustion was assumed, standard EPA F-factors were comparable in magnitude to the values generated by the real-time algorithm. The modified F-factor method was used to evaluate the gross heat rate. The resulting heat rate values were identical to those obtained by a real-time performance monitoring algorithm for the same input data. The modified F-factor method was likewise used to calculate the mass flow rate of CO2 as a function of gross plant generation. Those resulting values were compared to similar data reported to EPA. The real-time CO2 mass flow rate data obtained using the modified F-factor method agreed more closely with the EPA F-factor values as the plant load increased.