An asymmetry of vertical bending moment which occurs on ships having extreme flare on its bow shape is attributed to two reasons. One is the change of pressure distribution around ship's hull induced by advancing speed. This component can be significant for high speed ships, e. g. container ships. The other is nonlinear wave forces which consist of a shift of mean value and high-harmonic components. Calculation methods for estimating these components are presented respectively. Hess & Smith's method are made use of for estimating the component caused by advancing speed. This calculation can describe well the behavior of experimental data which varies widely from hogging to sagging depending on ship's hull form in the lower speed range. As for nonlinear wave forces, the effect of wave pressure force upon ship side slope is taken into account to give the shift of mean value and bi-harmonic component. This method is easily combined with the ordinary strip method to facilitate to calculate nonlinear wave forces. Calculation is compared with experimental data for these wave related components. These calculation and experimental data also show that the asymmetry of vertical bending moment is scarcely seen for ships of blunt shape but is dominant for ships having extreme flare.