The valuable ecosystem services of salt marshes are spurring marsh restoration projects around the world. However, it is difficult to forecast the final vegetated area based on physical drivers. Herein, we use a 3D fully coupled vegetation-hydrodynamic-morphological modeling system (COAWST), to simulate the final vegetation cover and the timescale to reach it from various forcing conditions. We found that marsh formation can be divided in three distinctive phases: a preparation phase characterized by sediment accumulation in the absence of vegetation, an encroachment phase in which the vegetated area grows, and an adjustment phase in which the vegetated area remains relatively constant while marsh accretes vertically to compensate for sea level rise. Sediment concentration, settling velocity, Sea Level Rise and tidal range each comparably affect equilibrium coverage and timescale in different ways. Our simulations show that The Unvegetated-Vegetated Ratio (UVVR) also relates to sediment budget in marsh formation under most conditions.