A full spectrum fitting code, developed and used by the Bath positron group to compute the fractions of positrons annihilated from surface, defect and bulk states as a function of incident positron energy, is described. To date, the most useful application of the code has been in studies of ion-implanted silicon, being particularly useful in the observation of the formation of oxygen-divacancy complexes. The advantages and limitations of the code are discussed. (c) 2005 Elsevier B.V. All rights reserved.