March 0

March 0 is an imaginary date. This formulation may be used in software such as Microsoft Excel to refer to the last day of February as a way of allowing for the fact that its length varies in leap years. It can also be used as a term for half-birthdays of people born on August 29, 30 and 31.

"March 0" is sometimes used by astronomers as a synonym for the last day of February.