Abstract Mild wear in gears is in most cases a smooth process giving initially improved contact conditions followed by a very slow and mild wear process. In some cases the mild wear may cause unfavorable changes of the surface topography, giving non-uniform gear rate, increasing dynamic effects and perhaps more severe forms of tooth failures. The knowledge about the interactions between mild wear, dynamic effects and other severe failures is rather limited. This paper therefore treats mild wear of spur gears, how it can be simulated and the effects of the same on contact conditions. A numerical model for wear prediction of spur gears is developed. The model can adopt any wear model although in this paper the wear simulations are based on a generalized Archard's wear equation. The running conditions for gear tooth surfaces are particularly considered and the contact between the surfaces are modelled by Winkler's elastic foundation model.