This master's thesis evaluates the cost-effectiveness of self-produced electricity in M-Real power plant in Simpele, Finland. Evaluation is especially focused on the cost-effectiveness of condensate electricity production. Evaluation is done by calculating incremental costs which consist of fuel and discharge costs. Due to the low power to heat ratio in the power plant thecost effectiveness is evaluated by dividing the power and heat production coststo products using the proportional method. The aim of this work is to find themost cost-effective mixed fuel ratio within given edge conditions. This is achieved by forming a calculation model where fuel costs are taken into consideration. The calculation model is optimized with the aid of the solver-function included in Microsoft Excel. The incremental costs of condensate electricity production are compared to the Nord Pools SPOT price per hour. Self-produced condensateelectricity is cost-effective if the daily average of the SPOT price per hour remains greater than the incremental costs.