Calculates the difference between two date values. The result returns the number of days between the two days.
Date_1 is the start date, Date_2 is the end date. If Date_2 is an earlier date than Date_1 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.