I use a plain text file with columns separated by tabulations. First column is my earning, and my expenses that are predictable (like phone, loan...). second column is my expenses on a daily basis. A simple awk command and I can compute a projection of the money that will be left on my account at the end of the month. Each month I use a new file. The beauty is that I can print the result of my command and put it in my status bar, next to the temp of my proc. It's a metric value like another after all.