Number of days between two dates

number-of-days-between-two-dates.el

(defun number-of-days-between-dates (date1 date2)
"Returns the number of days between two dates. 

 Usage:
     
     (number-of-days-between-dates \"yyyy-mm-dd\" \"yyyy-mm-dd\")

 Or

     M-x number-of-days-between-dates"
  (interactive "sStart Date (in yyyy-mm-dd format): \nsEnd date (in yyyy-mm-dd format): \n")
  (message
   (number-to-string
    (abs
     (- (time-to-day-in-year (date-to-time (concat date1 " 00:00:00")))
        (time-to-day-in-year (date-to-time (concat date2 " 00:00:00"))))))))