  The Littlest Seesaw (LS) model involves two right-handed neutrinos and a very
constrained Dirac neutrino mass matrix, involving one texture zero and two
independent Dirac masses, leading to a highly predictive scheme in which all
neutrino masses and the entire PMNS matrix is successfully predicted in terms
of just two real parameters. We calculate the renormalisation group (RG)
corrections to the LS predictions, with and without supersymmetry, including
also the threshold effects induced by the decoupling of heavy Majorana
neutrinos both analytically and numerically. We find that the predictions for
neutrino mixing angles and mass ratios are rather stable under RG corrections.
For example we find that the LS model with RG corrections predicts close to
maximal atmospheric mixing, $\theta_{23}=45^\circ \pm 1^\circ$, in most
considered cases, in tension with the latest NOvA results. The techniques used
here apply to other seesaw models with a strong normal mass hierarchy.
