Quantitative modeling of magmatic differentiation is a powerful tool that allows for the investigation of the chemical evolution of igneous rock suites. Numerous studies on the partitioning of elements between crystals and melts and the thermodynamics of magmatic systems have enabled modeling of mineral compositions from coexisting melt compositions using the methods described by Langmuir and Hanson (1981). Some modeling techniques have progressed such that the programs predict not only the compositions of the crystallizing minerals but also what phases are crystallizing and in what proportions. Examples of these types of programs include Magfox (Longhi, 1991), COMAGMAT (Ariskin et al., 1993), and MELTS (Ghiorso and Sack, 1995). While these programs are quite useful for estimating phase equilibria they do not always produce the best fit to datasets from comagmatic suites. The purpose of the Excel-based Visual Basic program (MagPath) presented here is to give users the ability to specify crystallization sequences and phase proportions that are not bound by known phase diagrams and free energy relationships. It is not intended to replace the constraints imposed by phase equilibria, but rather provide a more interactive means to decipher the various parameters that affect the compositional evolution of comagmatic rock suites.