This activity is presented as a guided lesson. The included PowerPoint presentation supports the teaching of functions in Microsoft Excel to students who have already used values in the application. In addition, the starter workbook file and assignment key are included. As the instructor actively teaches students to write mathematical functions in Excel using the presentation as a necessary visual aid, students update the starter file to calculate monthly expense data. Then, the student uses their learned knowledge to independently complete the starter file by adding the final remaining functions to make calculations for expenses paid.