This paper addresses the effect of formation length and service frequency on the determination of train timetables. The case of inter-city rail transport is considered since the planning of through journals allows the problem to be significantly simplified. Based on the analysis of passengers’ generalized travel expense, the law of passenger boarding choice considering the schedule delay cost is studied and extended. Then the law of boarding choice under the condition of the generalized travel cost is found. The law states that the distribution of the expected boarding time of passengers on every train is sequential, continuous and symmetric and the attractiveness range of each train is uniform. A maximum profit model with elastic demand is solved using an analytic method. A numerical example is provided to show the effects of train formation and service frequency on passenger demand and objective functions as well as the train schedule with different balance factors. Two operator service strategies (i.e. a short train and high service frequency mode or a long train and low service frequency mode) are analysed in depth.