To conduct effective and. efficient HAZOP (Hazard and Operability) study it is essential that the study should be planned and managed well. The planning and management can be done effectively only when the various steps of the study, scope of each step, and duration of each step are well defined. Significant,work has been done over the identification of various applications of HAZOP, but not much work has been done over HAZOP study duration estimation, which is a key parameter for proper-planning acid management of HAZOP study. Freeman at al. (1992) [6] have proposed a model for HAZOP study time (duration) estimation, however, it still needs modification in terms of easy application and more reliable estimation. The present work is an effort in the same direction, a mathematical model being proposed to forecast (estimate) the HAZOP study duration for varying capacity and complexity of-the problem. The accuracy of the results; has been checked with some of the past case studies carried out by various agencies. It has been observed that the authors＇ model predicts result with accuracy of about 90-95%, while Freeman＇s model is restricted to 85-90%. Moreover, the proposed model is simple, easy to implement, and can be automated to software.