Calculate Age or Years Elapsed in an Apple Numbers Sheet

Often it is useful to show a person's age or years elapsed since a start date.  For example:

Hire Date: 4/1/2012 - Years of service: 1.5

Here's a formula for Numbers that will do the trick:

=IF(ISBLANK(cellReference),"",DATEDIF(cellReference,TODAY(),"D")/365.2425)

Replace the cellReference with the actual cell reference. i.e.: (A1) 

So here's the breakdown:

=IF(ISBLANK(cellReference),"" --- this checks to see if there is a start date in your referenced cell.  For example say your spreadsheet has a cell (A1) that holds a date of birth, but it is not yet referenced, this will result in an empty string. (Blank cell)

Otherwise, it calculates the years: DATEDIF(cellReference,TODAY(),"D")/365.2425)

DATEDIF compares two dates.

The first date is your cell reference i.e.: (A1)

The second is the current date according to your computer, iOS device: TODAY() returning the Day - "D"

Then the difference is divided by 365.2425 to get the number of years.  Set your cell to result in a number with one decimal place.

There you go!