Nowadays predicting transportation costs is more and more important. Most significant part of inland navigation's costs are the costs of fuel. Fuel consumption is related to operating conditions of ship's propulsion system and its resistance. On inland waterways the ship resistance is strictly related to the depth of the waterway. There is a tendency to build a formula that allows its user to calculate the resistance of any inland waterway vessel, but researches claim that most of them are accurate only for particular types of ships and/or operating conditions. The paper presents selected methods of calculating ship resistance on inland waterways. These methods are examined for different types of ships and different conditions using results of model tests. The performed comparison enabled selecting the best option for pushboats and pushed barge trains, but also showed that any of the tested methods is good enough to be used for calculating the resistance of motor cargo vessels. For this reason, based on known equations and using the regression method, the authors have formulated a new method to calculate the resistance of motor cargo vessels on limited waterway. The method makes use of ship's geometry and depth of waterway in relation to ship's speed. Correlating the ship's speed with its resistance and going further with fuel consumption, enables to calculate the costs of voyage depending on the delivery time. The comparison of the methods shows that the new equation provides good accuracy in all examined speed ranges and all examined waterway depths.