Magnetic interactions in ladder vanadates are determined with quantum chemical computational schemes using the embedded cluster model approach to represent the material. The available experimental data for calcium vanadate is accurately reproduced and the nature of the interladder interaction is established to be ferromagnetic. An analysis of the main contributions to the magnetic couplings is presented and the role of the covalently bonded apex oxygen is elucidated. In the sodium vanadate, the ground state configuration of the rungs is V-3d(1)-O-2p(5)-V-3d(1). We show that with this configuration good intrachain coupling constants are obtained for the high-temperature phase. The interchain coupling in NaV2O5 is predicted to be approximate to34 K, ferromagnetic in nature. (C) 2004 American Institute of Physics.