Calculating construction costs and times is one of the most important and demanding tasks in construction management and economics. To arrive at a realistic calculation base, valid data and information is constantly being sought for labor consumption rates, output rates, productivity, material consumption, volumes in stock, number of transport cycles, and cost and time parameters that must be estimated or calculated ex ante. Ultimately, final cost and time parameters must be determined on the basis of such considerations and calculations. Accurate figures must be stated or submitted at the end of any analysis. These depend on the complexity of the building and on the conditions prevailing at the actual work stages and rely on more or less uncertain input data. One possible solution to this issue is to consider ranges that can deliver final conclusions on determined values. To systematically consider ranges in input parameters, this paper concentrates on applying probabilistic calculation methods based on Monte Carlo simulations. Key outcomes of probabilistic calculations include histograms that are used to directly capture the chance/risk ratio relative to a specific (selected) parameter. This paper presents a practical example of calculating the labor consumption rate for shuttering works to highlight the significance of the chosen chance/risk ratio and to show how it can be integrated into the systematic decision- making process adopted by the parties involved in the project.