A simple algorithm was implemented in a spreadsheet program to simulate the circular dichroism spectra of proteins from their secondary structure content and to fit [alpha]-helix, [beta]-sheet, and random coil contents from experimental far-UV circular dichroism spectra. The physical basis of the method is briefly reviewed within the context of protein structure, and the mathematical aspects of the approach are given together with ready-to-use code and examples. The work illustrates the use of simple yet powerful programming tools for simulations and data analysis in class and provides a means to explore the circular dichroism spectra of proteins and the applications of this spectroscopic technique to the study of proteins. (Contains 2 tables and 4 figures.)