December 31 is the 365th day of the year (366th in
leap years) in the
Gregorian calendar. This date is slightly more likely to fall on a Monday, Thursday or Saturday (58 in 400 years each) than on Tuesday or Wednesday (57), and slightly less likely to occur on a Friday or Sunday (56). It is known by a collection of names including:
Saint Sylvester's Day,
New Year's Eve or Old Years Day/Night, as the following day is
New Year's Day. It is the last day of the year. The following day is
January 1 of the following year.