The paper presents an improved model that will be used to predict the timing of excessive corrosion-induced cover cracking for Reinforced Concrete (RC) structures in chloride or carbonated environments. An accelerated corrosion experimental programme measured concrete cover cracking for crack widths of up to 1.0 mm (0.039 in) for RC slabs based on various concrete covers, concrete tensile strengths and reinforcing bar diameters. A new empirical crack propagation model based on the test data is then developed. A correction factor for reinforcement confinement is proposed to account for bars located at edges and corners of RC structures. The effect of the high corrosion rate on the times to cracking is discussed and a correction factor applied to allow the cracking times to be adjusted for the lower corrosion rates generally found in RC structures. A statistical analysis of model accuracy is used to account for variabilities between model prediction and experimental data. The new predictive model is compared with existing models. The crack propagation model presented herein is an essential tool for assessing the time-dependent performance of RC structures subject to chloride or carbonation induced corrosion.