Boundary estimates for non-divergence equations in $C^1$ domains

We obtain boundary nondegeneracy and regularity estimates for solutions to non-divergence equations in $C^1$ domains, providing an explicit modulus of continuity. Our results extend the classical Hopf-Oleinik lemma and boundary Lipschitz regularity for domains with $C^{1,\mathrm{D}\mathrm{i}\mathrm{n}\mathrm{i}}$ boundaries, while also recovering the known $C^{1-\epsilon }$ regularity for flat Lipschitz domains, unifying both theories with a single proof.