February 29 is a date that usually occurs every four years, and is called leap day. This day is added to the calendar in leap years as a corrective measure, because the Earth does not orbit the sun in precisely 365 days. The Gregorian calendar is a modification of the Julian calendar first used by the Romans.
For example, in the formula DATE( 2008, 5, -15), the DATE function returns a datetime value equivalent to April 15th of 2008, because 15 days are subtracted from the beginning of May 2008 yielding a value of April 2008.
Â© Ted French. The DAYS360 function can be used in accounting systems to calculate the number of days between two dates based on a 360-day year (twelve 30-day months).The syntax for the DAYS360 function is: = DAYS360 (Start_date, End_date, Method). Start_date-the start date of the chosen time period. Ted French. The DAYS360 function can be used in accounting systems to calculate the number of days between two dates based on a 360-day year (twelve 30-day months).