Recent trends in market liberalization and increasing congestion in the European interconnected grid have motivated study of market parameters provided close to real-time. In this paper, we present a method to compute the available transfer capacities between multiple bidding zones, based on inner polytope approximation and formulated as a linear programming problem. The method considers constraints on physical network flow and uses linearization for efficient computation to enable use in the balancing timeframe. The behaviour of the algorithm is demonstrated using real case studies. This paper also presents a near-real time decision support tool developed using the proposed method. The tool is in operation in the control room of Swissgrid, the Swiss Transmission System Operator.