This article aims to promulgate the use of Microsoft Excel, one of the predominant spreadsheet applications, in the calculation of approximate functions by the method of spline polynomial interpolation. Cubic spline functions have demonstrated a remarkable suitability for the analysis of pharmacokinetic data of drugs with non-linear kinetic behavior or an unknown kinetic model, as well as general kinetic analysis, regardless of pharmacokinetic and compartmental models. It should be noted that cubic spline polynomials can be employed in determining a highly significant pharmacokinetic parameter - the area under curve (AUC), especially when the area measurement is not the principal intention, and the data is to be used for further research. Spreadsheet software is exceptionally pertinent to this kind of computation, as it delivers high precision and virtually instantaneous availability of the results. Moreover, this type of software possesses conspicuous flexibility, characterized by a real-time graphical representation and the capability to sustain user-created functions through a macro-language (VBA - Visual Basic for Applications) implemented in the program itself. 

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