In cementless total hip arthroplasty, long-term implant stability is achieved by bone ingrowth. The strength of the new bond gradually increases in time, due to bone maturation and progression of ingrowth. In finite element simulations, osseointegration generally is implemented as an instant change in the mechanical behavior of the implant–bone interface, although this is a simplified interpretation of the bone ingrowth process. The aim of the present study was to build on previous bone ingrowth simulations and propose a new methodology to simulate bone ingrowth as a time-dependent process. We developed an algorithm to calculate the strength of the local implant–bone bond based of the magnitude of interface micromotions and gaps in time. Our algorithm was subsequently tested in multiple hip reconstructions in which the bone quality and implant–bone contact area were varied. The results of the simulations showed that in the ideal situation (good bone quality and no interface gaps), 91% of implant area could achieve ingrowth, while in the worst case only 17% of implant area showed ingrowth. The initial contact area had a significant effect on ingrowth, overruling the effect of variations in bone quality. The progression of ingrowth had a stabilizing effect on adjacent regions, especially in the high contact area cases. Further development and validation of the presented algorithm requires more information on the nature of the relation between the ingrowth rate and the magnitude of micromotions and gap.