Yes, there is a 31st of December in the modern calendar almost every year.

What is 31st of December?

  • In the Gregorian calendar, 31 December is the 365th day of the year, or the 366th in leap years.
  • It is the last calendar day of the year, immediately followed by 1 January of the new year.

Names and celebrations

  • 31 December is widely known as New Year’s Eve, marked by parties, fireworks, and countdowns around the world.
  • In many Christian traditions it is also called Saint Sylvester’s Day, with evening celebrations linked to that name in parts of Europe.

Fun calendar quirks

  • While 31 December exists as a date, there have been rare historical exceptions where specific places skipped that date during calendar adjustments (for example, the Philippines jumped from 30 December 1844 straight to 1 January 1845 to realign timekeeping).
  • Beyond the literal calendar, “December 31” is often used in pop science and culture, such as the “cosmic calendar” analogy where the whole history of the universe is compressed into one year and 31 December represents the very latest part of cosmic time.

TL;DR: If you are asking “is there a 31st of December?” on a normal calendar, the answer is yes—every year ends on that date in the standard Gregorian system.

Information gathered from public forums or data available on the internet and portrayed here.