Abstract Radiative feedback from luminous, massive stars during their formation is a key process in moderating accretion on to the stellar object. In the prior papers in this series, we showed that one form such feedback takes is UV line-driven disc ablation. Extending on this study, we now constrain the strength of this effect in the parameter range of star and disc properties appropriate to forming massive stars. Simulations show that ablation rate depends strongly on stellar parameters, but that this dependence can be parameterized as a nearly constant, fixed enhancement over the wind mass-loss rate, allowing us to predict the rate of disc ablation for massive (proto)stars as a function of stellar mass and metallicity. By comparing this to predicted accretion rates, we conclude that ablation is a strong feedback effect for very massive (proto)stars which should be considered in future studies of massive star formation.