Loved the article on what you're teaching your son about money. Thanks for including the example excel spreadsheet. Any chance you'd be willing to share the formulas you used to populate the cells? I'm not great with Excel, and apparently, not so great with math, either. I can get the spreadsheet to calculate monthly interest, but can't figure out how to let it calculate interest based on number of days, as you show in your example.
Any help is appreciated!