The paper presents an analysis of the actual change in brightness of comet 2I/Borisov. The calculations take into account total scattering cross-sections coming from ice, dust particles, and their combinations. It was assumed that dust particles are so-called silicate agglomerates which consist of single monomers. We analyze the actual outburst of the interstellar comet 2I/Borisov in terms of mass loss. This parameter (mass ejected) is one of the main factors determining the amplitude of the comet’s brightness jump. A numerical model was developed and used to analyze the loss of mass ejected during the cometary outburst 2I/Borisov. The calculations presented in this paper are related to the actual outburst of comet 2I/Borisov which was observed in March 2020 with a change in brightness Δm = −0.7 magnitude. The ratio of the mass of thrown dust to the mass of ejected ice, which determines the observed change in brightness, was also determined. In the case of water ice controlled sublimation, the ratio is between 9.51 and 8.16. However, in the case of the sublimation of carbon monoxide, this parameter takes values from 7.47 to 3.07. The values of these mass ratios are significantly related to the η(t1) parameter.