Abstract This paper expounds a revised characterisation of the elastic stresses ahead of a crack tip in polycarbonate which takes account of the elastic–plastic boundary stresses induced by the presence of the crazed region that surrounds a crack. The advanced experimental techniques used in this work have provided insights into fractography, identification of the crazed region and location of the crack tip position (using confocal laser scanning microscopy and scanning electron microscopy). In addition, the four-parameter model of crack tip stresses has led to modified definitions for crack tip stress intensity factors which explicitly account for craze-induced shielding effects on the fatigue crack growth rate in polycarbonate. The model is generic and offers the potential for increased understanding of fatigue crack growth in polycarbonate.