The initial, non-stationary stage of silver electrocrystallisation during the potentiostatic reduction of silver thiosulphate complexes was investigated in this work. Curve fitting based on known nucleation and growth laws does not give reliable results. It was suggested therefore that the formation of subcritical 2D silver clusters, preceding the formation of supercritical, stable 3D nuclei, and their growth must be seen as two simultaneously occurring phenomena, both consuming a certain amount of current. An analytical expression that takes this into account is introduced and evaluated with the experimental results. From the obtained fitting parameters the steady state nucleation rate and the total number of nuclei are determined as a function of the applied potential.