To predict the service life of welded joints, the seam welds of samples (cross joint, K-seam, sheet thickness 15 mm and a laser-welded butt joint, sheet thickness 6 mm, both made of steel quality S 355) are recorded using a 3D scanner. The data obtained in this way is processed and transferred to a finite element method program. The meshing of the weld seams is very detailed. A finite-element-method stress calculation is then carried out. The real samples are tested in a fatigue test up to the point of cracking. The results from calculation and test are then compared. A possible crack location can be predicted very well using the finite element method results. The cracks in the real test are always in the area of very high or often the absolute highest calculated stresses. A prediction of the service life in the fatigue test is possible with a certain scatter – close to the usual scatter for welded joints. Based on the results of 19 samples, a fatigue class for local stress (based on the real geometry) of FAT 300 can be preliminary estimated for the cross-joint specimens. Definition according to the specifications of the International Institute of Welding (FAT at 2 mio. cycles, survival probability 97.7 %).