Formation of cracks in a material as a result of the damage accumulation may change (weaken) material effective properties. The present letter suggests an approach to estimate such changes when cracks form at interfaces of dissimilar materials (for example, at matrix/inclusion boundaries or film/substrate interfaces). Generally, solution of an interface problem is required to predict compliances of interfacial cracks, with the exception of planar cracks. We show that planar cracks possess a special property in the sense that their normal compliances may be approximated from solutions in a homogeneous medium. The method is then applied to analyze elastic compliances of the rectilinear, penny-shaped, elliptical, and annular interfacial cracks. (C) 2005 American Institute of Physics.