We use density functional theory to calculate the structure, band-gap and magnetic properties of oxygen-deficient SrTi1−x−yFexCoyO 3−δ with x = y = 0.125 and δ = {0, 0.125, 0.25}. The valence and the high or low spin-states of the Co and Fe ions, as well as the lattice distortion and the band-gap, depend on the oxygen deficiency, the locations of the vacancies, and on the direction of the Fe-Co axis. A charge redistribution that resembles a self-regulatory response lies behind the valence spin-state changes. Ferromagnetism dominates, and both the magnetization and the band gap are greatest at δ = 0.125. This qualitatively mimics the previously reported magnetization measured for SrTiFeO 3−δ , which was maximum at an intermediate deposition pressure of oxygen.Reprinted with permission from