We propose a practical algorithm for calculating Heisenberg exchange integrals, J, in multispin systems using broken-symmetry methods. Our generalized spin-projection (GP) method is an extended version of the approximate spin-projection (AP) method for two-spin systems. A notable feature of GP is its wide application for chemical bonds in magnetic materials, from covalent bonds to biradical bonds. The GP algorithm is applied to several transition metal complexes. The results show that this method effectively works for calculation of J values and is reliable in characterizing the detailed magnetic properties of multi-nuclear metal complexes. (c) 2006 Published by Elsevier B.V.