Gregorian calendar

For the calendar of religious holidays and periods, see Liturgical year. For this year's Gregorian calendar, see Common year starting on Thursday.

Not to be confused with Georgian calendar.

Today (at UTC+00)
Thursday, 10 September 2026
Gregorian	10 September, AD 2026
Other calendars Akan Nkyiyaw Armenian 22 Hoṙi 1476 Aztec Tititl 3, 10 Ozomahtli Babylonian 27 Abu, 2337 SE Balinese pawukon Menga, Kajeng, Sri, Keliwon, Urukung, Wraspati of Menail, Ludra, Gigis, Manusa Bengali 26 Bhadro, BS 1433 Chinese Yin Fire Pig・Well Mansion 29 Qīyuè, Bǐngwǔnián (Bailu, 13 days until Qiufen) Common Era 10 September 2026 CE Coptic 5 Nesi, AM 1742 Egyptian 27 Tybi, 2775 NE Ethiopian 5 Pāguemēn, 2018 Amätä Məhrät French Republican Décade III, Quartidi de Fructidor de l'Année 234 de la République Gregorian 10 September, AD 2026 Hebrew 28 Elul, AM 5786 Hindu Maghā・Siddha Solar: 25 Bhādrapada, 1948 SE Lunisolar: Caturdaśī, Kṛishna pakṣa of Śrāvaṇa, 2083 VE Rāudra・5127 KY・1,872,828 Icelandic Fimmtudagur, 17 Tvímánuður 2026 Islamic 27 Rabi' al-awwal, AH 1448 (using tabular method) ISO week date 2026-W37-4 Japanese 29 Fumizuki, Reiwa 8 (Hakuro, 13 days until Shūbun) Julian 28 August, AD 2026 (AM 7534) Julian day 2461294 Maya 13.0.13.16.11 4 Chen, 10 Chuen Roman ante diem V Kalendas Septembres, MMDCCLXXIX AUC Solar Hijri 19 Shahrivar, SH 1405 Tibetan 29 gro bzhin, me pho rta 2153 or 1772 or 1000
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The Gregorian calendar is the calendar currently used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years slightly differently to make the average calendar year 365.2425 days long rather than the Julian calendar's 365.25 days, thus more closely approximating the 365.2422-day tropical, or solar, year that is determined by the Earth's revolution around the Sun.

The rule for leap years is that every year divisible by four is a leap year, except for years that are divisible by 100 but not also divisible by 400. For example, 1800 and 1900 were not leap years, but 1600 and 2000 were.

There were two reasons to establish the Gregorian calendar. First, the Julian calendar was based on the estimate that the average solar year is exactly 365.25 days long, an overestimate of a little under one day per century, and thus has a leap year every four years without exception. The Gregorian reform shortened the average (calendar) year by 0.0075 days to stop the drift of the calendar with respect to the equinoxes. Second, in the years since the First Council of Nicaea in AD 325, the excess leap days introduced by the Julian algorithm had caused the calendar to drift such that the March equinox was occurring well before its nominal 21 March date. This date was important to the Christian churches, because it is fundamental to the calculation of the date of Easter. To reinstate the association, the reform advanced the date by 10 days: Thursday 4 October 1582 was followed by Friday 15 October 1582. In addition, the reform also altered the lunar cycle used by the Church to calculate the date for Easter, because astronomical new moons were occurring four days before the calculated dates.

The reform was adopted initially by the Catholic countries of Europe and their overseas possessions. Over the next three centuries, the Protestant and Eastern Orthodox countries also gradually moved to what they called the "Improved calendar", with Greece being the last European country to adopt the calendar (for civil use only) in 1923. However, many Orthodox churches continue to use the Julian calendar for religious rites and the dating of major feasts. To unambiguously specify a date during the transition period (in contemporary documents or in history texts), both notations were given, tagged as "Old Style" or "New Style" as appropriate. During the 20th century, most non-Western countries also adopted the calendar, at least for civil purposes.