By selecting the month and entering the integer day of the month and the integer year, this equation will provide the day of the year. You must specify the year to determine if its a leap year.
For example:
Enter January 9 2015 and the equation outputs 9
Enter January 9 2016 and the equation outputs 10 (because its a leap year)
Enter April 4 2014 and the equation outputs 94
Enter April 4 2016 and the equation outputs 95 (because its a leap year)
Enter September 11 2011 and the equation outputs 254
Enter December 31 2015 and the equation outputs 365
Enter December 31 2016 and the equation outputs 366 (because its a leap year)