The main objective of this work is to propose a method based on Monte Carlo simulation (MCS) to estimate the allocation of project cost contingency reserves in the planning phase, incorporating the different types of uncertainty described in the literature, associating them to each of the risks identified in the project. The method was applied to validate our proposal on an actual construction project carried out by the University of Valladolid (Spain). Applying the proposed method has allowed us to obtain a more accurate estimate of cost contingencies than the method traditionally used by the company, which consisted of reserving a fixed and arbitrary percentage of the total project execution budget. Keywords: Monte Carlo Simulation; Quantitative Risk Analysis; Cost Contingency; Risk Management; MCSimulRisk