The outer rise is a topographic bulge seaward of the trench at a subduction zone that is caused by bending and flexure of the oceanic lithosphere as subduction commences. The classic model of the flexure of oceanic lithosphere w(x) is a hydrostatic restoring force acting upon an elastic plate at the trench axis. The governing parameters are elastic thickness T-e, shear force V-0, and bending moment M-0. V-0 and M-0 are unknown variables that are typically replaced by other quantities such as the height of the fore-bulge, w(b) , and the half-width of the fore-bulge, (x(b) - x(o)). However, this method is difficult to implement with the presence of excessive topographic noise around the bulge of the outer rise. Here, we present an alternative method to the classic model, in which lithospheric flexure w(x) is a function of the flexure at the trench axis w(0), the initial dip angle of subduction beta(0), and the elastic thickness T-e. In this investigation, we apply a sensitivity analysis to both methods in order to determine the impact of the differing parameters on the solution, w(x). The parametric sensitivity analysis suggests that stable solutions for the alternative approach requires relatively low beta(0) values (<15 degrees), which are consistent with the initial dip angles observed in seismic velocity-depth models across convergent margins worldwide. The predicted flexure for both methods are compared with observed bathymetric profiles across the Izu-Mariana trench, where the old and cold Pacific plate is characterized by a pronounced outer rise bulge. The alternative method is a more suitable approach, assuming that accurate geometric information at the trench axis (i.e.w(0), and beta(0)) is available.