The mass number of the reactant, 236U, is 236. Because the actual mass is , its mass excess is +. Calculated in the same manner, the mass excess for the products, 92Kr, 141Ba, and three neutrons, are , and , respectively, for a total mass excess of . The difference between the mass excess of the reactants and that of the products is , which shows that the mass excess of the products is less than that of the reactants, and so the fission can occur – a calculation which could have also been done with only the masses of the reactants.