The kinetic crystallization model of Avrami is generally accepted as a starting point for the analysis of isothermal polymer crystallization. However, in most cases, the experimental situation is complicated by an incubation time prior to isothermal crystallization, so that the Avrami equation must be modified. Moreover, the experimental data are often limited in number and restricted to an intermediate crystallinity range. Furthermore, data of isothermal crystallization experiments performed at different temperatures, cannot be evaluated together by using an evaluation procedure being based on the Avrami equation. An iterative procedure and a crystallization-temperature independent Avrami master curve, which overcome these problems if the Avrami index n is bigger than one, are displayed in this work.