In the Genesis flood account, how long did rain fall on the earth?

In the Genesis flood account, rain fell on the earth for forty days and forty nights.

Genesis 7:12 uses this phrase to describe the period of rainfall after Noah, his family, and the animals entered the ark. The same forty-day period is repeated in Genesis 7:17 when describing the rising floodwaters. It is one of the best-known time markers in the Noah story.

The forty days of rain should not be confused with the total time that the floodwaters covered the earth. Genesis also says that the waters prevailed for 150 days, and the narrative continues through the ark’s resting, the sending of birds, and the drying of the ground. Those figures describe different stages of the story.

The number forty also appears elsewhere in the Bible in periods of testing or transition, including Moses’ time on Mount Sinai and Israel’s wilderness journey. In Genesis, however, the rainfall period is specifically forty days and forty nights.