An equation for the decrease of stabilizer content in propellants is given, which describes the measured consumption of stabilizers such as diphenylamine, 2-nitrodiphenylamine, acardite II and ethylcentralite very well. The equation was obtained with a kinetic formulation for the stabilizer depletion, which combines the reactions of first and zero order. According to this model, the times up to a complete consumption of the stabilizer are finite (they are infinite if the decrease is purely exponential), and can be calculated with the reaction rate constants of the model. The prediction of the life times is considerably improved. This new equation allows a normalized representation of the stabilizer decrease, which can reveal mechanistic changes in the course of the reaction.