During the tensile testing of the specimen on a biaxial horizontal tensile tester, there is deformation not only in the specimen itself but also in the structure of the tensile tester due to the reaction force. This means that the displacement of the actuator used to stretch the specimen causes deformation not only in the specimen but also in the overall structure. Although this deformation is small, it should not be neglected as it could impact the execution of experiments and the determination of material properties of the test specimen. By using a correction factor, the displacement of the actuator can be automatically adjusted to ensure that the achieved strain in the test specimen is equal to the desired value. The objective of this paper is to determine the necessary correction using the finite element method (FEM), with the application of the Abaqus® software, on the geometry of the tensile tester with lowered clamps and on the geometry with raised clamps. Before the numerical analysis itself, the fundamentals of materials and their testing are presented in the introductory chapter of the paper. In the second chapter, the basics of biaxial tensile testing, types of specimen grips, experimental procedures and the constitutive model are presented. The third chapter provides a brief description of the working principle of the biaxial horizontal tensile tester and the concept of the study. The fourth chapter outlines the basics of the finite element method and the Abaqus® software. The modeling procedure in the Abaqus® software is described in the fifth chapter, and the analysis results for both geometries are presented, considering complete structural models as well as models without legs. In the sixth chapter, corrections for both geometries are determined in the form of correction diagrams and the equation of the line that describes the lines on the diagrams.