The plastic behavior of BCC metals shows a pronounced dependence of non-glide or non-Schmid stresses acting on the crystal lattice; this phenomenon tends to make the material prone to develop non-associated plastic flow. The constitutive description of crystal plasticity via the phenomenological modelling approach and the finite element method enables the computational study of deformation occurring at both the microscopic and macroscopic scales of the material. However, these approaches establish criteria based on the conventional material behavior of FCC structures via Schmid law, in which dislocation movement initiates when the resolved shear stress acting only on glide systems reaches the lattice resistance and ignores the contribution of non-glide stresses. Thus, this work proposes a multiscale methodology based on theories of non-Schmid crystal plasticity to model deformation in BCC metals by yield surface analysis. To predict the plastic behavior of the material, we first simulate the tensile properties of single crystal pure iron using experimental data reported in the literature. The model is calibrated using stress-strain diagrams by implementing a non-Schmid crystal plasticity subroutine with a finite element analysis software, performing an inverse analysis based on Efficient Global Optimization (EGO) techniques to construct the yield surface of single crystals. A statistically informed Representative Volume Element (RVE) is performed to determine the polycrystal yield surface by modelling multiaxial strain paths and determining the effective micromechanical response. The parameters of a Cazacu-Barlat type macroscopic yield criterion are obtained using a least-squares optimization technique. The results suggest that the non-Schmid effect incorporated into the crystal plasticity formulation alters the number of active slip systems concerning the Schmid law, being the critical factor of plastic behavior. Finally, this study opens a strategy to systematically investigate the contribution of the non-Schmid stresses on the yield onset and the flow behavior in BCC metals.