This study presents a thermoeconomic analysis methodology to calculate unit energy (electricity and heat) production cost for a combined cycle system with steam extraction (cogeneration system). The aim of this methodology is to find the minimum energy production cost. Therefore, firstly, minimum electricity production cost is found by using annual levelized cost method for a combined cycle system which only produces electricity. Secondly, minimum heat production cost for a combined cycle system with steam extraction is calculated. Extracted steam causes the power loss in the steam turbine and reduces the income. So, heat energy production cost can be correctly determined. In the model, the fall of the income associated with the power loss is accepted as equal to heat energy cost, and heat energy production cost is formulated as a function of electricity energy production cost. Finally, the effect of different parameters like compressor pressure ratio and steam pressure on heat production cost is investigated. As a result, the outcomes of this study can provide a basis used for determination of the unit energy production costs for different energy production systems.