The paper deals with the estimation of the lifetime of structures in high-cycle fatigue. The methodology adopted is a multiscale approach based on the following points: (i) at the macroscopic scale, the material is in elastic shakedown; (ii) at the mesoscopic scale the material presents an elastic shakedown (infinite life), or a plastic shakedown or ratcheting (finite life); (iii) the material behavior, at the mesoscopic scale, is hydrostatic stress dependent due to crack nucleation processes; (iv) damage is governed by the mesoscopic accumulated plastic strain per stabilized cycle. The model has six parameters. A simplified version and a robust identification procedure are proposed. A validation by comparing simulated lifetimes to experimental ones is carried out.