Best Fit of Cumulative Cost Curves at the Planning and Performed Stages of Construction Projects

The correct planning of investment costs and the effective monitoring of implementation process are significant problems in the management of investment projects. At the stage of construction works, it is worth determining the trend of the performed cost curve and periodically testing the fitting to the scheduled course of the budgeted cost curve. The aim of this research was to determine the shape and course of the cost curves for selected construction projects. A procedure was developed to forecast the distribution of cumulative costs at the planning stage of construction projects using envelopes (spaces) and cost curves for three different types of buildings and construction sectors: collective residential buildings, hotel buildings, and commercial and service buildings. An assessment of the actual costs incurred of investment tasks was carried out, the trend of which the cumulative cash flow curves can be estimated with a large match by forecasting the construction process. The article determines the best fit curves and the spaces of cost curves (the banana envelope of the S-curve) using mathematical formulas (third-degree polynomials), along with developed graphs for various construction projects. The analysis of the author’s own research was used to determine the best-fit curve and the curve’s area, which indicates the area of the correct planning of cumulative costs of construction investments.