The nature of dark matter particle is one of the biggest puzzles in physics today. Gamma-rays (as measured by e.g. Fermi LAT NASA satellite) are particularly powerful ways to test one of the most popular particle physics proposal, WIMPs. However, to test particle physics properties via gamma-rays, dark matter clustering along a line of sight needs to be known. In this work we use the latest knowledge from N-body simulations of DM clustering to update the predictions of gamma-ray signal from dark matter annihilation in all dark matter halos at all redshifts, the so-called cosmological dark matter signal. This works makes part of the ongoing work within the Fermi LAT collaboration, which aims to update the search for the dark matter cosmological signal, previously performed in 2015. In the introductory chapters we review the basics of the $Lambda$CDM standard model of cosmology, the physics of DM clustering and its potential gamma-ray signals. We then focus on the calculation of the DM clustering contribution to the gamma ray signal, the so called flux multiplier $zeta$. We describe the two different approaches to calculating its value - the Power Spectrum approach, and the Halo Model approach. We discuss the technical aspects of both approaches and describe the quantities used in each of them with the aim to improve the existing results by using the state-of-art value for different functions, which became available since the last work in 2015. In the context of the halo model approach we prepare the machinery to re-evaluate theoretical prediction of DM signal that depends on DM clustering and derive the first results. In the context of the power spectrum approach, we measure the power spectrum of the full-box Lomonosov simulation and compare our results with the power spectrum measured of the Millennium and Millennium II simulations.