In the case of step-growth polymerisation of monomers carrying functional groups of the same type (so called  polymerisation) the degree distribution is given by:  where  is bond conversion,  is the average functionality, and  is the initial fractions of monomers of functionality . In the later expression unit reaction rate is assumed without loss of generality.  According to the theory, the system is in the gel state when , where the gelation conversion is . Analytical expression for average molecular weight and molar mass distribution are known too. When more complex reaction kinetics are involved, for example chemical substitution, side reactions or degradation, one may still apply the theory by computing  using numerical integration. In which case,  signifies that the system is in the gel state at time t (or in the sol state when the inequality sign is flipped).