Calculators allow to estimate the costs of building projects with regard to the price determination. They are an important guide for engineers and architects in setting their fees. A calculation aid should be based on empirical data collected in the form of a survey by the SIA. Statistical modeling of hourly working time on projects will provide a basis for predicting bandwidths for future project fees. Since a prediction is also subject to uncertainty, a prognosis interval is additionally indicated in each case. The size of the forecast intervals will of course also vary according to the type, effort and construction costs of a project.The goal is to find a data-pruned model that is based on statistically estimated parameters.