A simplified method for approximating precompound nuclear reaction effects in Hauser-Feshbach codes for the calculation of double differential (n, xn) cross sections is presented. The method is developed from an existing quantum mechanical formula of unified compound and precompound reaction theories. The compound part of the unified formula is made identical to that of Hauser and Feshbach by applying the unified level-density formulas derived previously for the two theories. The precompound part, much more complicated than the compound part, is simplified and globally parameterized for practical purposes. Calculated double differential (n, xn) cross sections at 14 and 26 MeV for iron, niobium, and bismuth are shown to be in good agreement with the available experimental data. The method at various stages of development has been applied with success to the generation of evaluated files of double differential (n, xn) cross sections from 5 to 20 MeV for the major isotopes of chromium, manganese, iron, nickel, and copper.