This paper presents a mathematical multi-criteria quantitative construction risk management tool which aims at capturing cost increase due to changes of a project at various stages of construction providing a real time phase-sensitive risk index. A mathematical risk management model was designed to mimic three types of activity alterations from the original construction project plan in the course of a phased construction schedule. Project data with three types of changes were employed to demonstrate the real time mathematical risk model associated with phasing of a construction project. The results show that the construction mathematical risk management tool was able to evaluate and monitor discrete and cumulative project risk for construction project managers providing major benefits in terms of contextualising various types and natures of changes that bring about construction project risk. The model offers practical considerations in that the move in industry towards monitoring each phase of a project resulting in a real time phase-sensitive and dynamic risk monitoring can be supported by an approach such as this. Equally, there is scope for enhancing the approach through development of a risk management knowledge base tool. The originality of this paper lies in its uniqueness in a systematic approach to multi-criteria risk management monitoring development to construction contextualised with project management body of knowledge to capture risk as discrete and cumulative approach for real time phase-sensitive risk index.