A numerical optimization model was developed to investigate the impact of sex (entire, castrated or GnRH vaccinated males, and females) on optimal slaughter weight of pigs. Non-linear animal performance curves were fitted based on the data of growth trials. Sex-specific performance curves (growth and cumulative feed intake) were incorporated into the model. Monte-Carlo simulation was executed to simulate the distributions of the parameters in the performance curves. For each iteration in the Monte-Carlo simulation the economic optimal slaughter weight, resulting in the largest annual gross margin per fattening place, was calculated for a basic economic scenario. The results suggest important differences between sexes in optimal slaughter weight and annual gross margin when fattened separately. Future extensions to the pig pricing model should refine these results. The next step is to investigate how results change when gilts are finished with another sex on the same location and the optimization has to be aggregated at the barn level instead of optimizing at the level of the sex.