In Genesis, on what day of Noah’s life does the floodwaters begin?

In Genesis, the floodwaters begin on the 17th day of the second month of Noah’s six-hundredth year.

Genesis 7:11 gives the date using Noah’s age and a calendar reference: in the six hundredth year of Noah’s life, during the second month, on the seventeenth day, the fountains of the deep burst open and the windows of heaven open. The passage therefore supplies a precise narrative date.

This is different from the question of how long the rain falls. Genesis gives several flood-related time spans, including the forty days and forty nights of rain, the period the waters prevail, and later dates for the waters receding. These figures describe different stages and should not be treated as interchangeable.

The text does not identify the calendar system in modern terms, so converting the date to a current month and day would go beyond what Genesis states.