A pseudohelical approximation for the calculation of the bandstructures of DNA base homostacks in B conformation is introduced. It consists of choosing a unit cell of only two nucleobases with relative parallel displacement and twist that locally mimic the helical conformation. It is tested employing the extended Hückel method with a unique Wolfsberg-Helmholtz parameter. The resulting bandgaps and ionization potential trend agree well with the ones reported in the literature employing the full screw-axis symmetry and higher levels of theory. The electron and hole effective masses extracted from the bandstructures follow the same trends as the experimentally reported mobilities.