In many industrial applications it is necessary to predict fatigue lifetime of the structures where the stress field near the crack front have a three-dimensional nature. Due to the existence of vertex singularity in the point where the crack front touches free surface, crack propagation in 3D structures cannot be reduced to a series of plane strain or plane stress problems along the crack front. The paper describes the influence of the vertex singularity on crack shape for three-dimensional structure. The iterative process for estimation of a real crack front based on a stress singularity exponent is presented. In each node defining the crack front the stress singularity exponent has been estimated and complete crack front shape corresponding to the constant stress singularity exponent was found. The methodology presented can help to estimate crack front shape in a linear elastic fracture mechanics framework and estimate fracture parameters of fatigue cracks more accurately.