The main methods of calculation of the inelastic mean free path (IMFP), $\lambda$, of inelastically-scattered electrons versus their energy $E_{0}$ are reviewed. Mechanisms, which influence on the character of $\lambda($E_{0}$)$-dependence of IMFP, are considered for electron—electron scattering within the framework of the free electron-gas model approximation. Within the framework of the examined model, the IMFPs, $\lambda$, is calculated for pure Pt, Co and a Pt$_{80}$Co$_{20}$ alloy in a wide range of energies – $Е_0 = 10 − 1600$ eV. The obtained results are compared with experimental data on IMFPs, $\lambda$, for $3d$-metals (Fe $\rightarrow$ Cu) and $5d$-metals (Pt, Au). As revealed, the high divergence of experimental dependence and semi-empirical calculations for IMFP, $\lambda_{exp}$, is in the low-energy range of $Е_0$. As shown, a most correct definition of IMFP, $\lambda(Е_0)$, may be obtained by approximation of experimental data, if any, by $\lambda = A / E_{0}^{2} + BE_{0}^{1/2}$ relation (where $A$, $B$ are fitting parameters).