DATEDIFF
DATEDIFF([Created On], [Completed On], 'year')Syntax
DATEDIFF(start date, end date, date part)
Returns the count of the specified date part boundaries crossed between the specified start date and end date.
start date: Date calculation created using date functions, data fields or constants.
end date: Date calculation created using date functions, data fields or constants.
date part: Text constant which can be chosen from minute, hour, day, week, month, quarter, year