The article describes the methodology for calculating the economic efficiency of the modifications and upgrades of freight wagons. This process involves updating the fixed assets of the railway transport, equipping the existing rolling stock with modern equipment, using domestic and foreign innovative developments. The main components of the integral effect obtained during the modernization of the rolling stock of railways are described. The economic evaluation of projects aimed at modernization using innovations must be carried out taking into account the mathematical model in the form of a problem of optimization of a linear function with restrictions. The aim of the study is to develop the methodological foundations of the economic assessment of the modernization of freight wagons. Evaluation of economic efficiency is an important stage in the project to develop a complex of new generation freight wagons with improved technical and economic indicators, which the authors are engaged in.