A new semi-empirical equation for the dependence of transference numbers upon concentration is reported. It is a simple equation applicable to many electrolytes of different stoichiometry over large molality ranges. The equation for each electrolyte is characterized by four parameters, one of them (J(i)) being the transference number at infinite dilution, another two (D-i, L-i) lacking physical meaning, and the fourth being an integer or semi-integer fixed parameter (p(i)=1/2, 1, 3/2). For some electrolytes, the last parameter can be different for cation and anion. An apparent incoherence of the proposed equation has been solved by using Taylor series and also by non-linear regression analysis followed by smoothing. As a consequence of this, the equation now reported is of dual application for either the cation or the anion transference numbers. Some applications of the new equation to obtain hydration and water transference limiting numbers besides isothermal compressibilities of electrolyte solution are presented.