Abstract. We prove time decay of solutions to the Muskat equation in 2D and in 3D. In [11] and [12], the authors introduce the normsin order to prove global existence of solutions to the Muskat problem. In this paper, for the 3D Muskat problem, given initial data f 0 ∈ H l (R 2 ) for some l ≥ 3 such that f 0 1 < k 0 for a constant k 0 ≈ 1/5, we prove uniform in time bounds of f s(t) for −d < s < l − 1 and assuming f 0 ν < ∞ we prove time decay estimates of the form f s(t) (1 + t) −s+ν for 0 ≤ s ≤ l − 1 and −d ≤ ν < s. These large time decay rates are the same as the optimal rate for the linear Muskat equation. We also prove analogous results in 2D.