Gregorian

Overview

The Gregorian Calendar is a calculated solar calendar used by most of the world. It has 365 days, with an extra leap day every year divisible by 4 unless divisible by 100, except for years also divisible by 400.

The era is denoted 'CE' meaning 'Common Era' and 'BCE' meaning 'Before Common Era'. Dates can also be expressed in AD/BC as in the Julian calendar.

The calendar was issued by Pope Gregory XIII on October 15th, 1582 and is derived from the Julian Calendar after skipping 10 days between October 5th and 15th. The two calendars differ by the 400-year leap year rule.

This calendar is exactly accurate, however dates before October 15th 1582 are proleptic, and many countries did not adopt it until much later than 1582.

Info

After the initial 10-day skip in 1582 and the following centuries to the 21st century, the Gregorian calendar and the Julian calendar are 13 days apart.

Accuracy

The Gregorian calendar is exactly accurate, as it is what this entire site is based on. However, it does drift from the solar year ever so slightly at a rate of about 1 day every 3030 years without taking axial precession into account, or 1 day every 7700 years if taken into account.

Source

All of the information on this calendar came from its Wikipedia article.