If you need to calculate dates in your spreadsheets, Excel uses its own unique system, which it calls Serial Numbers. Every date (month, day, year) and time (hour, minute, and second) has an ...

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.