January 0

fictional date conventionally used to indicate the day before January 1 in the same year, i.e. December 31 in the previous year

January 0 does not exist in any calendars. It sometimes refers to December 31.

In an ephimeris


January 0 also refers to the day before January 1 in an annual ephemeris. It keeps the date in the year for which the ephemeris was published. It avoids any reference to the previous year, even though it is the same day as December 31 of the previous year.



In Microsoft Excel, the epoch of the 1900 date format is January 0, 1900.[1]

Similar dates



  1. Lowe, Scott (May 11, 2007). "How do I... Perform basic formatting in Excel 2003?". TechRepublic.
  2. "A Classic Ray Bradbury Esquire Story". esquire.com. 6 June 2012. Retrieved 21 March 2017.