Relations to calculate estimated enthalpies of fusion of binary compounds and eutectics at their equilibrium temperature in binary systems of inorganic substances, based on entropy or enthalpy balances, are presented. Their simplified forms were applied to estimate the enthalpy of fusion of equimolar compounds and binary eutectics in the Na2SO4-NaF and K2SO4-KF systems. Estimated enthalpies of fusion of NaF . Na2SO4 and KF . K2SO4 depend on simplified assumptions used for the calculation and are 7-13% lower than measured values. Relative errors of estimated enthalpies of fusion for eutectics, related to the values of these quantities calculated using experimental heats of fusion of binary compounds and measured enthalpies of mixing at corresponding eutectic composition, are within the limits 0-12% depending on input quantities.