Calculates the difference between two date values. The result returns the number of days between the two days.
Date1 is the start date, Date2 is the end date. If Date2 is an earlier date than Date1 the result is a negative number.
=DAYS(NOW();"2010-01-01")) returns the number of days from January 1, 2010 until today.
=DAYS("1990-10-10";"1980-10-10") returns 3652 days.