This contribution critically evaluates the default allocation method between milk and meat proposed by the International Dairy Federation. Two aspects can lead to biased or incomplete results depending on the system investigated: 1) the linear approximation and 2) the exclusion of heifers sold to another dairy. We propose to calculate allocation factors based on the marginal net energy investments for 1 kg FCPM and 1 kg of average life weight gain, yielding values of 3.1 MJ/kg FPCM and 15-18 MJ/kg live weight. The allocation method between milk and meat in the dairy production proposed by IDF can be recommended, if BMR<3% and the whole dairy sector is investigated. For BMR>3%, alternative methods should be used to avoid underestimation of the environmental impacts of milk. If dairy production of a farm is analysed, also the heifers sold to other farms should be included in the outputs.