On what date did the Flood begin, according to Genesis?

According to Genesis, the Flood began on the 17th day of the second month of Noah’s 600th year.

Genesis 7:11 gives the date while describing the release of the fountains of the deep and the opening of the sky. Genesis 7:13 then describes Noah, his family, and the animals entering the Ark on that same day.

This is an internal date in the calendar used by the Genesis narrative, not a date that can be converted confidently into a modern calendar date. The text supplies the month and day but does not identify the calendar system in modern terms.

Genesis also gives other dates during the Flood account, including the Ark’s resting on the mountains of Ararat on the 17th day of the seventh month. Those two dates are separated by five months and should not be confused.