December 31 is the 365th day of the year (366th in leap years) in the Gregorian calendar. 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, the first day of the following year. It is also the last day of the fourth and final quarter of the year.