To calculate elastic moduli as obtained by nanoindentation in film/substrate systems, a ’hydrostatic-core’ model has been developed. The model,gives simple expressions for the transitional function, which describes the dependence of composite (effective) compliance on indentation depth. Since the model does not require an assumption of minor bending of the sample surface, it can be applied to plastically deformed, indented layered systems, with indentation depth comparable with the thickness of the film. The predicted transitional function is in agreement with recent experimental results of indentation of Al2O3/Al and Al2O3/sapphire systems when assuming that the longitudinal size of the hydrostatic core depends on the ratio of the Young modulus of the film and substrate.