  We present a next-to-leading order perturbative QCD calculation of dimuon
production in neutrino-nucleus collisions. This process is typically calculated
by assuming it to be proportional to inclusive charm production, which requires
an effective acceptance correction to take the experimental cuts on the
decay-muon kinematics into account. Here, we instead compute the dimuon
production cross section directly as a convolution of semi-inclusive deep
inelastic scattering to produce charmed hadrons, and a decay function fitted to
$e^+e^-$ data to produce a muon from the charmed hadrons. The presented
approach is in a good agreement with available experimental data and will serve
as a starting point for higher-order QCD calculations without an external
acceptance correction. The uncertainties arising from the decay function and
scale dependence are sizeably smaller than those from the nuclear parton
distribution functions. We also calculate the effective acceptances within our
approach and compare them to those usually used in global fits of parton
distribution functions, finding differences of the order of $10\,\%$, depending
on the kinematics, perturbative order, and applied parton distributions.
