What 12-month calendar date is New Year's Eve?

New Year's Eve is December 31 in the Gregorian calendar, the day before New Year's Day.

The date is observed from the evening of December 31 until midnight, when the calendar changes to January 1. Celebrations often include a countdown, meals, music, fireworks, religious services, and gatherings with family or friends. The exact local moment of midnight differs around the world because time zones enter the new date at different times.

The Gregorian calendar was introduced by Pope Gregory XIII in 1582 as a reform of the Julian calendar. It is now the civil calendar used in most countries, although many cultures also observe New Year dates based on other calendars. Consequently, “New Year’s Eve” can refer to different dates in traditions such as the Lunar New Year or Rosh Hashanah.

In ordinary international usage, however, the phrase refers to December 31. January 1 is New Year’s Day, not New Year’s Eve, even though celebrations often continue after midnight.