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The critical magnetic field is one of the most interesting properties of superconductors. Thus, this study aimed to investigate the surface and upper critical magnetic fields of superconductors in Fe-based and cuprate superconductors as KFeSe and LaSrCuO superconductors, respectively. The anisotropic two-band Ginzburg–Landau method was used to generate the analytic equation. The analytics were shown for the simplified equation so that a second-order polynomial temperature-dependent equation could be applied and fitted to the experimental results of KFeSe and LaSrCuO superconductors. After that, numerical calculations were applied to find the shape of the Fermi surface, which is an important component within the band structure. It was found that the anisotropy of the Fermi surface for each band structure was affected by the upper critical magnetic field and the surface critical magnetic field to the upper critical magnetic field of the superconductors. The second-order polynomial temperature-dependent model can be applied to other superconductors to predict the surface and upper critical magnetic fields. [ABSTRACT FROM AUTHOR]