AbstractDisruptive events are the main source of delays in projects. A key task for construction managers is to revise the project schedule plan based on time delays caused by these events. Consequently, project management research has developed various forecasting methods to evaluate the prospective impact of disruptive events on project completion time. This article tackles three shortcomings of the available forecasting methods: (1) the extrapolative and judgmental nature of these methods, (2) the lack of an explicit focus on project resources, and (3) the lack of attention to the disproportionate impact of disruptive events on project resources. The method developed in this study takes into account the detrimental effects of disruptive events on project resources in the case where there is no historical precedence. In this method, project resources are first mapped into reliability block diagrams (RBDs) to develop a stochastic variable that reflects the impact of resource shortages on project activity. A Monte Carlo simulation analysis is performed to simulate the uncertainty in acquiring resources during disruptions. The impact of resource shortages on the completion time of project activity is then quantified by means of the stochastic variable developed in the first step. The proposed method is demonstrated in a real-life construction project. The validation results prove the better performance of the new method in forecasting time delays caused by unexpected events compared to the existing methods. The proposed method assists construction managers in revising project schedule plans and provides benefits in framing and solving problems that arise when disruptions occur.