Another source of information will be the bills and receipts that you have received over the past quarter. If you have not kept such documents and records before, then now is a good time to start. The good organisation of your important financial documents, and orderly filing of bills and receipts, will stand you in good stead for controlling the family budget when it is set.
Back during the infancy of this software, most people would use it for just two reasons: to store data (especially customer database) and as a glorified calculator. Perhaps because those are a spreadsheets intended or more practical uses or that people are not really that trained to use its features to the fullest. You would even be surprised that up to now there are office employees who, when they are prompted to make some calculations, they would open their spreadsheet software and do the calculations there. However, as weird as that may sound, it is one of the ways that a spreadsheet can help speed things up in the office. Especially if the employee has been working on spreadsheets for a long time that making fast calculations using the cells has become second nature to him. But there are other good uses for this application.