A little over a year ago, I discussed the obscure

**DateDif**function, and it was a readers’ favorite.As I mentioned in my 2009 post, Microsoft has for reasons only they know, mysteriously chosen not to include documented information of this

**fascinating function**in Excel.**DateDif**is a very useful (I think it is essential) tool for doing calculations with dates. Here is a refresher with some additional good information.The syntax of the function is as follows:

**=DateDif(First Date, Second Date, Time Interval)**

Where the

**is expressed as follows:**

*Time Interval***d**(Days) = Number of days between the dates

**m**(Months) = Complete calendar months between the dates

**y**(Years) = Complete calendar years between the dates

**Note:**The

**must be greater than the**

*Second Date***, or you will get a**

*First Date**.*

**Number Error**An entertaining application of this function is to nest the

**NOW()**function into it and calculate a person’s age as follows (Note: the “BirthDate” can refer to an easily changed cell value):

**=DateDif(BirthDate, NOW(), “y”)**

**Special Note:**If you put the

**in the function directly, be sure to put “quotation marks” around it (e.g.**

*Time Interval***“m”**). If you put it into the formula via a cell reference, do not use the quotation marks (e.g. the cell should contain

**m**, not

**“m”**).

There are a great many ways to use the

**DateDif**function, so give it a try some time.

**You may wonder how you ever lived without it!**