There is little sound information about the impact of cow genetic selection programs on whole farm profit. We analyse aggregate industry data to identify trends in dairy herd genetic, production and reproductive performance. We model genetic distribution within herds over time from a long-term genetic selection program and use a representative whole-farm bioeconomic (simulation) model to explore the impact of herd genetic change on profit of the case farm. Analysis of an industry herd recording database reveals an average annual rate of increase in Balanced Production Index (BPI) of 7 units for the herd (2.9 and 10.1 for the bottom and top BPI quartiles) and 10.8 BPI units for artificial insemination sires used within herds. Modelling these trends for herds with an age-cohort BPI range average of 43 units of BPI and 20% cohort attrition rates show that the natural range between bottom and top BPI quartiles expands gradually but remains between 75–100 units in most herds across 50 years of selection. Bioeconomic modelling found an average of around $2,500 extra contribution to farm profit per annum for the 250-cow herd representative farm, with the herd achieving an annual rate of increase in herd BPI of around 10 units per year. These findings indicate that comparing performance of BPI quartiles within herds provides almost no insight into impacts of genetic selection on farm profit. Applying more widely the findings and insights from modelling genetic gain in representative pasture-based dairy farm suggests it is likely that that on many, or even most dairy farms, the gains in profit from cow genetic selection may be modest. Good advice to dairy farmers would be to (i) have realistic expectations about the role of genetic gain in their business; (ii) evaluate returns from investment in herd genetics; and (iii) compare expected returns from investments into all limiting factors present on the farm.