Ab initio calculations based on density functional theory have been employed to study energetic, structural, electronic, and optical properties of Cr doped Bi4Ge3O12 (BGO). Two possible accommodations of Cr impurity have been taken into account: at the Ge (Cr4+) and the Bi (Cr3+) substitution site. For each accommodation the local structure around the Cr has been determined, and in the Cr3+ case the Cr off-site displacement was analyzed. The Cr d-states are positioned at the bottom of the conduction band and within the gap in form of two deeplike (Cr4+) and shallowlike (Cr3+) bands, exhibiting magnetic moments of +1.58 μB and −2.44 μB, respectively. The Cr dominated part of absorption spectrum is calculated and analyzed in terms of Cr band arrangement. Comparison with the experimental BGO:Cr absorption spectrum suggests that it consists of both Cr3+ and Cr4+ contributions, indicating the Cr simultaneous presence at both substitution sites