A challenge in the field of polymer network synthesis by a step-growth mechanism is the quantification of the relative importance of inter- vs. intramolecular reactions. Here we use a matrix-based kinetic Monte Carlo (<i>k</i>MC) framework to demonstrate that the variation of the chain length distribution and its averages (e.g., number average chain length <i>x_n</i>), are largely affected by intramolecular reactions, as mostly ignored in theoretical studies. We showcase that a conventional approach based on equations derived by Carothers, Flory and Stockmayer, assuming constant reactivities and ignoring intramolecular reactions, is very approximate, and the use of asymptotic limits is biased. Intramolecular reactions stretch the functional group (FG) conversion range and reduce the average chain lengths. In the likely case of restricted mobilities due to diffusional limitations because of a viscosity increase during polymerization, a complex <i>x_n</i> profile with possible plateau formation may arise. The joint consideration of stoichiometric and non-stoichiometric conditions allows the validation of hypotheses for both the intrinsic and apparent reactivities of inter- and intramolecular reactions. The <i>k</i>MC framework is also utilized for reverse engineering purposes, aiming at the identification of advanced (pseudo-)analytical equations, dimensionless numbers and mechanistic insights. We highlight that assuming average molecules by equally distributing A and B FGs is unsuited, and the number of AB intramolecular combinations is affected by the number of monomer units in the molecules, specifically at high FG conversions. In the absence of mobility constraints, dimensionless numbers can be considered to map the time variation of the fraction of intramolecular reactions, but still, a complex solution results, making a <i>k</i>MC approach overall most elegant. We showcase that a conventional approach based on equations derived by Carothers, Flory and Stockmayer, assuming constant reactivities and ignoring intramolecular reactions, is very approximate, and the use of asymptotic limits is biased. Intramolecular reactions stretch the functional group (FG) conversion range and reduce the average chain lengths. In the likely case of restricted mobilities due to diffusional limitations because of a viscosity increase during polymerization, a complex x n profile with possible plateau formation may arise. Due to the nature of the step-growth polymerization mechanism with a gradual formation of dimers ( x = 2), trimers ( x = 3) and ultimately x -mers with x >> 1, a high extent of reaction and thus FG conversion (>>0.95) is required to achieve high average chain lengths [ 1 , 14 ]. Impurities and molar imbalances, which are often aggravated by different volatility tendencies, have a deleterious effect on the quality of the final polymer product. This equation is based on general stochastic insights and gives the degree of polymerization or number average chain length, i.e., x n , for a given (A or equivalently B) FG conversion p with r = 1 ignoring intramolecular reactions: (1) x n = 1 1 − p This equation reaches an asymptotic value at p = p * = 1 and requires, in practice, a final evaluation at p = 0.99. The monomers AA and BB (or AB) are considered having a chain length of 1, and it is assumed that potential byproduct is removed from the reaction mixture so that equilibrium settings can be ignored (so-called kinetically controlled step-growth polymerization) [ 19 ]. For branched step-growth polymerization systems, Carothers [ 18 ] modified his original equation stating that x n is dependent on the average functionality per monomer f av (Equation (6); f a v = N m o n , A , 0 f A + N m o n , B , 0 f B N m o n , A , 0 + N m o n , B , 0 with N mon , A ,0 and N mon , B ,0 being the initial number of monomer molecules based on FG A and B, respectively, and f A and f B the related functionality degrees, respectively). The equation is limited to stoichiometrically balanced reactions ( r = 1), describing the synthesis up to the asymptotic value located at p* = 2/ f av , which is denoted as the critical degree of FG conversion. Nevertheless, chain length averages can still be determined without first determining the CLD, and more recent results have been reported by Beginn et al. [ 33 ] and Cheng et al. [ 34 , 35 ]. Hillegers et al. [ 36 ] used, in turn, this approach to calculate path length—the number of chemical bonds in the path connecting two monomeric units in a molecule—distributions in an A 1 + A 2 + A 3 type polymerization. However, the technique based on Equation (12) involves abstract mathematics and, as such, is difficult to use. Figure 5 Benchmark between equations derived by Flory [ 22 ] and/or Stockmayer [ 27 , 28 ] (black) and the kinetic Monte Carlo ( k This is done by evaluating the effect of k i n t r a V N a v k i n t e r on the number average chain length x n as a function of the A FG conversion ( p A ); the Flory equation [ 22 ] (Equation (9); ρ = 1) is depicted as a grey dashed line; subplot ( b ) is a zoom of ( a ) for a small p A range with a 5% deviation from the equation by Flory, additionally indicated by a fuchsia dashed line; k intra/inter : intra/intermolecular rate coefficient; V : simulation volume; N Av : Avogadro number; k MC simulations based on Figure 3 . 3.2. Focus is on the effect of the number average chain length x n as a function of the A FG conversion p A (left axis; solid lines) for different ratios of k i n t r a V N A v k i n t e r and different r values: ( a ) k i n t r a V N A v k i n t e r = 1.0 × 10 − 2 and r = 1, ( b ) k i n t r a V N A v k i n t e r = 1.0 × 10 − 2 and r = 0.75, ( c ) k i n t r a V N A v k i n t e r = 1.0 and r = 1 and ( d ) k i n t r a V N A v k i n t e r = 1.0 and r = 0.75. Also given are the conventional results according to Equation (9) (Flory equation [ 22 ]; black line; no intramolecular reactions).