In the Genesis flood narrative, rain fell on the earth for forty days and forty nights.
Genesis 7:12 gives this duration after Noah, his family, and the animals entered the ark. The same chapter separately describes the floodwaters prevailing for a much longer period, so the forty days of rain should not be confused with the total length of the flood episode.
The number forty has wider symbolic importance in biblical literature. Other examples include Moses’ forty days on Mount Sinai and Israel’s forty years in the wilderness. In the ark story, however, the text uses it specifically to describe uninterrupted rainfall.
The Genesis account also says that the fountains of the deep opened, presenting the flood as coming from both rain above and waters below. Thus, forty days refers to the rain, not to the complete time Noah spent aboard the ark.