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The constraint plays an important role in the fatigue design of mechanicalcomponents. In particular, the global constraint factor αg is the most usedparameter in the field of fatigue to evaluate the level of constraint at the crackfront and it is a crucial parameter in wide spread algorithms.The present work aims to address how to obtain reliable values of constraint toemploy in fatigue crack growth simulations, in order to improve the predictions ofcrack propagation models such as the Strip-Yield model.A novel approach is presented for the calculation of the global constraint factor,based on the evaluation of local field parameters (J-integral, T-stress) and cyclicmaterial properties. The model was set up on typical fracture mechanics andfatigue test specimens, then applied to the evaluation of the constraint state aheadof cracks in a railway axle