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${\mathrm{CoFe}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{NiFe}}_{2}{\mathrm{O}}_{4}$ are well-known insulating ferrimagnetic spinel ferrites with high Curie temperatures, an important characteristic for electronic spintronic applications. We used first-principles calculations to investigate how their magnetic properties can be altered or tuned by the presence of structural point defects. considered successively effects cation distribution in lattice stoichiometric compounds atom substitutions vacancies. Our demonstrate that a deviation from perfectly inverse cations increases magnetization decreases width band gap at Fermi level. In contrast vacancies, oxygen vacancies not expected strongly affect magnetization. show crystals excess Ni display spin-polarized hole conductivity. finally calculated formation energy different defects we give details on states.