The aim of this work was to show the dependence between the time needed for the equilibrium calculations as well as convergence of the method in dependence on the distance between the tie line and the plait point for three most widely used binary prediction methods: NRTL, UNIQUAC and modified UNIQUAC. Recognition of these dependencies is crucial for the choice of the computational method in extraction calculations. Four various ternary systems were used as examples. The uniform criterion for ceasing the calculations was described together with the discussion of its influence on the course of the equilibrium calculations. For calculations a special application was used.