The invention relates to a process for determining a molecular weight distribution in a polymer. When a polymer is prepared, chains of different length are formed. Correspondingly, a distribution of the molecular weights of the chains of a polymer arises. It is an object of the invention to be able to determine the molecular weight distribution in an improved manner compared to the prior art. The object of the invention is achieved by describing starting data G*(ω) available in numerical form, i.e. the complex shear modulus measured as a function of frequency or the mastercurve constructed therefrom, are described by an analytical function. In this way, exact knowledge of the relaxation behaviour is available in improved form, in particular also in the case of prolonged relaxation times. This enables a valid determination of the relaxation time spectrum and hence a fundamentally more valid calculation of the molecular weight distribution.