With wide proliferation of Information technology (IT) in modern business, IT expenditure has become a regular yet strategic decision for most senior management. In this short article, we propose a model to explain the determinants of IT budget. Built upon the pioneer work by Dewan et al.  and Kobelsky et al. , we attempted to extend the prior research by providing a strong theoretical underpinning for the driving forces of IT budget, incorporating both dynamic and static contingencies from internal organization as well as external environment. The proposed model is aimed to provide a reference metric for IT budget decision.