Anno Mundi

Anno Mundi (from Latin 'in the year of the world'; Hebrew: לבריאת העולם, romanized: Livryat haOlam, lit. 'to the creation of the world'), abbreviated as AM or A.M., or Year After Creation, is a calendar era based on biblical accounts of the creation of the world and subsequent history. Two such calendar eras of notable use are:

• Since the Middle Ages, the Hebrew calendar has been based on rabbinic calculations of the year of creation from the Hebrew Masoretic Text of the Bible. This calendar is used within Jewish communities for religious purposes and is one of two official calendars in Israel. In the Hebrew calendar, the day begins at sunset. The calendar's epoch, corresponding to the calculated date of the world's creation, is equivalent to sunset on the Julian proleptic calendar date 6 October 3761 BCE. The new year begins at Rosh Hashanah, in Tishrei. Anno Mundi 5786 (meaning the 5,786th year since the creation of the world) began at sunset on September 22, 2025, according to the Gregorian calendar.
• The Creation Era of Constantinople was observed by Christian communities within the Eastern Roman Empire as part of the Byzantine Calendar and retained by Eastern Orthodoxy until 1728. Its Year One, marking the assumed date of creation, was September 1, 5509 BC, to August 31, 5508 BC. This would make the current year (AD 2026) 7534 (7535 after September 1).

While both eras reputedly begin with the creation of the world, their disparity in epoch lies in the biblical texts chosen to infer a year of creation. According to the Septuagint, the Earth seems to have been created roughly around 5500 BCE, and about 3760 BCE based on the Hebrew Masoretic text. Most of the 1,732-year difference resides in numerical discrepancies in the genealogies of the two versions of the Book of Genesis. Patriarchs from Adam to Terah, the father of Abraham, are said to be older by 100 years or more when they begat their named son in the Septuagint than they were in the Latin Vulgate, or the Hebrew Tanakh. The net difference between the two major genealogies of Genesis is 1,466 years (ignoring the "second year after the flood" ambiguity), 85% of the total difference. (See Dating creation.)

There are also discrepancies between methods of dating based on the text of the Bible vs. modern academic dating of landmark events used to calibrate year counts, such as the destruction of the First Temple—see Missing years (Jewish calendar).