A simulation model that is able to investigate hypotheses about dairy cow fertility is presented here. Over the last decades, in parallel with changes in genetics, productivity and management, dairy cattle have faced a decline in fertility. A number of possible physiological mechanisms underlying the decline in reproductive efficiency have been proposed, with a major focus on the interaction between lactation, nutrition and reproduction. However, given that fertility can be impaired on different levels (e.g. oocyte quality, oestradiol levels, uterine health), there is no clear consensus on how mechanisms like negative energy balance or increased milk yield in itself impair fertility in dairy cows: everything is connected to everything. The model presented here combines a simple reproductive physiology model, where each step in the fertility cycle is represented separately, with an existing animal model of lifetime performance based on a conceptual representation of energy partitioning. The reproductive physiology model incorporates genetic, endocrine, metabolic and stochastic regulatory components, meaning that at each step in the fertility cycle the individual effects of animal factors on that step can be adjusted. The resulting whole model allowed us to test hypotheses on the animal factors modulating reproduction, like milk potential, parity or energy balance. The model can easily be adjusted when new insights are achieved, based on the compartmental nature and the different regulatory components. Model outputs are in good agreement with findings reported in literature, suggesting that it adequately represents the major effects of cow performance on reproduction. This model provides a way to quantify the effects of impaired fertility on long term productive performance.