A realistic computer model is presented for calculating the time‐dependent volume fraction transformed during the devitrification of glasses, assuming the classical theory of nucleation and continuous growth. Time‐ and cluster‐dependent nucleation rates are calculated by modeling directly the evolving cluster distribution. Statistical overlap in the volume fraction transformed is taken into account using the standard Johnson–Mehl–Avrami formalism. Devitrification behavior under isothermal and nonisothermal conditions is described. The model is used to demonstrate that the recent suggestion by Ray and Day,1that nonisothermal DSC studies can be used to determine the temperature for the peak nucleation rate, is qualitatively correct for lithium disilicate, the glass inv