In this paper I will illustrate how to extend the capabilities of Microsoft Excel spreadsheets with add-ins created by MATLAB. Excel provides a broad array of fundamental tools but often comes up short when more sophisticated scenarios are involved. To overcome this short-coming of Excel while retaining its ease of use, I will describe how MATLAB's Excel-Builder converts MATLAB functions into Excel macros. The add-ins can be freely distributed and operate solely from Excel. To demonstrate the utility of add-ins, I will describe a project that I am currently working on in Excel that could be enhanced with the add-ins to carry out more sophisticated scenarios. The project deals with the question of when a person approaching retirement age should begin accepting social security. [For complete proceedings, see ED490093.]