The durability and the life of spot welded sheet metal structures are mainly controlled by the strength of the joints. Designers are aiming at reliable information, already in early design phase, that the weld spots will indeed perform satisfactorily throughout the required life cycles of a complex structure under the operational loading conditions. Consequently, a theoretical approach for the determination of the structural durability and the reliable design and optimization of spot welded components has been developed and extensively verified for serial components by theoretical analysis and tests. The method starts with Finite-Element-computations of the structures in the design stage and strength data obtained from component-like specimens; both are commonly available in the design phase, but are not sufficient for the determination of the structural integrity. The developed calculation procedure subsequently allows the determination of the local stresses that may lead to fatigue cracks in spot welded joints and the respective local endurable strength. Therefore the method is suitable for routine fatigue life calculations of structures with multiple weld spots and individual local loading conditions. In order to provide a ready tool on a routine basis to the design engineers a software was developed to be used as a Finite-Element post processor (FESPOW-Fatigue life Evaluation of SPOt Welds). Thus already in the design phase a spot welded structure can be optimized with regard to strength, weight and cost for manufacturing, testing as well as development.