  We investigate the growth factor for sub-horizon modes during late times in
$f(T,\mathcal{T})$ gravity, where $T$ is the torsion scalar and $\mathcal{T}$
is the trace of the stress-energy tensor. This is achieved by obtaining the
modified M\'{e}sz\'{a}ros equation, which describes the evolution of the
perturbations of the matter energy density, and obtaining numerical results.
Such results are obtained by solving the modified continuity equation and
analysing the behaviour of the solutions of the latter using various
constraints on the integration constants. Furthermore, the role of the
anisotropic term $\pi^{S}$ is investigated.
