Gregorian calendar
What is the Gregorian calendar?
Why was the Gregorian calendar created?
When was the Gregorian calendar adopted?
What’s the difference between the Gregorian and Julian calendars?
Does the United States use the Gregorian calendar?
Gregorian calendar, solar dating system now in general use. It was proclaimed in 1582 by Pope Gregory XIII as a reform of the Julian calendar.
By the Julian reckoning, the solar year lasts 365 1/4 days, and the intercalation of a “leap day” every four years was intended to maintain correspondence between the calendar and the seasons. However, the solar year more precisely lasts 365 days, 5 hours, 48 minutes, and 45.25 seconds—that is, more than 11 minutes shorter than 365 1/4 days. This slight inaccuracy accumulated and caused the calendar dates of the seasons to regress by almost one day per century.
Although this regression had amounted to 14 days by Pope Gregory’s time, he based his reform on restoration of the vernal equinox, then falling on March 11, to March 21, the date it occurred in 325 ce, which was the time of the First Council of Nicaea and not the date of the equinox at the time of the birth of Christ, when it fell on March 25. The change was effected by advancing the calendar 10 days after October 4, 1582, the day following being reckoned as October 15.
The Gregorian calendar differs from the Julian only in that no century year is a leap year unless it is exactly divisible by 400 (e.g., 1600 and 2000). This change means that a year is 365.2425 days long in the Gregorian calendar. In the 21st century the solar year is 365.24237 days, and thus the Gregorian calendar is about 11 seconds ahead of the solar year. The seasons now advance by only one day in about 7,700 years. A further proposed refinement, the designation of years evenly divisible by 4,000 as common (not leap) years, would keep the Gregorian calendar accurate to within one day in 20,000 years.
- Also called:
- New Style calendar
- Key People:
- Gregory XIII
- On the Web:
- The Galileo Project - The Gregorian Calendar (Apr. 02, 2026)
In 1699 Sweden decided to adopt the Gregorian calendar gradually by dropping leap years between 1700 and 1740. The leap year was dropped in 1700. However, that year Sweden went to war with Russia in the Second Northern War, and the government’s preoccupation with the war is credited with the 1704 and 1708 leap years being retained and not dropped as the 1699 plan intended. Sweden then had its own calendar that was 10 days behind the Gregorian and one day ahead of the Julian. King Charles XII put Sweden back on the Julian calendar by adding a second leap day, February 30, in 1712. Sweden finally switched to the Gregorian in 1753 by dropping the 11 days between February 17 and March 1.
Within a year the change had been adopted by the Italian states, Portugal, Spain, and the Roman Catholic German states. Gradually, other countries adopted the Gregorian calendar: the Protestant German states in 1699, Great Britain and its colonies in 1752, Sweden in 1753, Japan in 1873, China in 1912, the Soviet socialist republics in 1918, and Greece in 1923. (The growing discrepancy between the Julian and Gregorian calendars meant that countries that switched later had to drop more days. Great Britain dropped 11 days in 1752. Greece dropped 13 days in 1923.) Islamic countries tend to use the Gregorian calendar for secular life but retain calendars based on Islam for religious purposes (see Islamic calendar).
