One of the many features of Excel is being nosy. That's right, you can quickly calculate a persons age as long as you have their birth date.

The easy part: Age in days Zee’s need is similar to that of business spreadsheet users who need to calculate the age in days of unpaid invoices. Zee’s date of entry is like the invoice date.

Percentages aren't always easy to calculate, but one of the best tools in Excel's toolbox is calculating percentages for you. Here's how to do it.