On what day of the month did the biblical Flood begin?

The biblical Flood began on the 17th day of the second month.

Genesis 7:11 dates the start of the Flood precisely: it says that in Noah’s six hundredth year, during the second month, on the seventeenth day, the fountains of the deep burst open and the windows of heaven were opened. This is one of the account’s most specific calendar references.

The date belongs to the chronology used by the Genesis narrative and should not be treated as a securely convertible date in the modern Gregorian calendar. The text also uses a month-and-day system without giving enough information to map it to a modern year.

Later dates continue the sequence. Genesis says the Ark came to rest on the mountains of Ararat on the seventeenth day of the seventh month, exactly five months after the Flood’s dated beginning in the narrative. The account therefore combines theological storytelling with unusually detailed chronological markers.