According to Genesis 7:4, rain was announced for forty days and forty nights in the Flood story. The passage says that this rainfall would wipe away living things from the land.
The number forty has a recurring role in biblical narratives, often marking an extended period of testing, transition, or preparation. Other biblical examples include Moses’ periods on Mount Sinai and Jesus’ forty days in the wilderness, though those events belong to different books and traditions.
The forty days of rain are not the same as the total duration of the Flood. Genesis also says that the waters prevailed for 150 days and later describes a long process of recession and drying.
This distinction matters because retellings often summarize the entire Flood as lasting forty days. In Genesis, forty days refers specifically to the announced rain period.