Density-based sorting is the most commonly applied method to sort plastic waste from Electrical and Electronic Equipment (WEEE) and End-of-Life Vehicles (ELVs). Therefore, density-based sorting processes have a large influence on the volumes of plastics that get recycled, incinerated and landfilled. However, the optimal control of these processes is challenging, since both the composition of plastic waste streams and regulation on the treatment of plastic waste are ever evolving. To maximise the recycling potential of the treated plastic material, this article presents a method to assess the effectiveness of density-based sorting processes. Through lab-scale density separation experiments and spectroscopic measurements, the polymer type concentrations and the chlorine and bromine levels are determined in function of density for four fractions of plastics that are either landfilled, incinerated or recycled after density-based sorting. Based on the results, changes are recommended to the operation of the sorting processes.