How long does Genesis say rain falls during the flood in Noah's Ark story?

Genesis says rain falls for forty days and forty nights during the flood in Noah's Ark story.

Genesis 7:12 gives the duration of the rain as forty days and forty nights. The narrative also says the floodwaters prevail on the earth for a much longer period, so these are not interchangeable measurements. Rain stops after forty days, but the waters continue to cover the land and later recede.

Genesis separately mentions that the waters prevail for 150 days. That figure describes the continuing dominance of the floodwaters rather than the period of rainfall itself. Confusing the two numbers is one of the most common ways to misstate the chronology.

The number forty also appears in several other biblical narratives, including Moses' time on Mount Sinai and Israel's wilderness period. That recurring biblical number does not change the specific flood statement: the rain lasts forty days and forty nights. The answer should include both the number and the traditional time phrase because Genesis uses the complete expression.