The DATEDIF function is a mystery function within Excel. When you write it out in a workbook it doesn’t give you any hints like other functions would and if you look it up in the function list you would not find it! Creepy…
The DATEDIF function stands for “date difference” and it calculates the number of Days, Months, or Years between two dates.
So if you want to find out how many days, years or months have passed since you were born, well this is the formula for you! Well you can also extend this to project start and end dates, but you get my point.