Weld bead geometry cannot, by its very nature, be precisely defined. Parameters such as bead shape and toe radius vary from joint to joint even in well-controlled manufacturing operations. In the Notch Stress Intensity Factor (N-SIF) approach the weld toe region is modelled as a sharp V-shaped corner and local stress distributions in planar problems can be expressed in closed form on the basis of the relevant Mode I and Mode II N-SIFs. Initially thought of as parameters suitable for quantifying only the crack initiation life, N-SIFs are shown able to predict also the total fatigue life, at least when a large part of the life is spent as in the propagation of small cracks in the highly stressed region close to the notch tip. A large amount of experimental data reported in the literature for steel and aluminium welded joints is used here to demonstrate the applicability of the N-SIF-based approach.