  For inflation driven by the Higgs field coupled non-minimally to gravity, we
study the cutoff energy scale above which perturbation theory breaks down.
Employing the metric formulation, we first give an overview of known results
and then provide a new way to calculate a lower bound on the cutoff. Our
approach neither relies on a gauge choice nor does it require any calculation
of amplitudes. Instead, it exploits the fact that the S-matrix is invariant
under field redefinitions. In agreement with previous findings, we demonstrate
that the cutoff is significantly higher during inflation than in vacuum, which
ensures the robustness of semi-classical predictions. Along the way, we
generalize our findings to the Palatini formulation and comment on a useful
parametrization of the Higgs doublet in both scenarios.
