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 and other purposes. On 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 BC.
The new year begins at Rosh Hashanah, in Tishrei. Year anno mundi 5781, or AM 5781, began at sunset on 18 September 2020 on the Gregorian calendar.