Skewness of implanted ion profiles is determined by extending the Biersack model to higher-order terms. Nuclear and electronic energy losses up to the fourth moment are included in the skewness equations to yield better results for any ion-target combination. The feasibility of the proposed skewness equations is examined using profiles of various ions implanted into target materials of up to two constituents. Calculated skewness values correlate well with experimental data. Kurtosis values calculated using Biersack's fitting formula also closely correspond to experimental data.