DATEDIF(), which means Date + Dif, is a compatibility function left over from Lotus 1-2-3 that Microsoft adopted in Excel version 2000, which is the only version that explains how this function works. It’s operational in all Excel versions, but it’s not on the Formulas menu or in the Help menus after Excel 2000. If your spreadsheet experiences began with Lotus, which is true for many thousands of users, you’ll be happy to know that this old Lotus function is still alive and kicking.
The purpose of this function is to calculate the time between a user-specified starting and ending date in days, months, or years. The arguments for this function are: