The present invention is designed to efficiently calculate isotopic distribution in order to simulate mass spectra data for any chemical compound of interest. The simulated spectra considers the various isotopes of the compound based upon a probability calculation that takes into consideration the natural abundance of each isotope of individual elements of the compound. The probability calculation generates a relative probability associated with each isotope species of the subject compound. The simulated spectra are displayed on an x-y coordinate illustrating the calculated formula weight on the abscissa (x-axis) and the intensity of the specific species on the ordinate (y-axis). This theoretical data is then compared to experimental data taken from a mass spectrometer in order to identify the chemical compound at issue.