How many days and nights of rain does Genesis say began the Flood?

Genesis says rain fell for forty days and forty nights at the beginning of the Flood.

Genesis 7:12 states that rain fell upon the earth for forty days and forty nights. The number 40 is a recurring period in biblical narratives, often associated with testing, transition, or preparation. Examples include Moses’ periods on Mount Sinai and Jesus’ fast in the wilderness, although those episodes are separate from the Flood story.

The forty-day rain period is not the same as the entire duration of the Flood. Genesis also describes the waters prevailing for 150 days and records a much longer sequence before the ground became dry. This distinction explains why summaries sometimes give different numbers for the flood’s length.

The Genesis narrative combines the rain with subterranean waters described as the “fountains of the great deep.” Its account is a religious narrative, while scientific explanations of major ancient floods concern different geological and historical questions.