In the biblical Noah's Ark story, the Flood waters prevailed on the earth for 150 days.
Genesis uses several time markers to describe the Flood. Rain fell for forty days and forty nights, but the waters continued to rise or remain dominant afterward. Genesis 7:24 says that the waters prevailed on the earth for 150 days. The account then describes the waters beginning to subside and the Ark resting on the mountains of Ararat.
This distinction is one of the most commonly confused chronological details in the story. Forty days refers to the period of rain, while 150 days refers to the period during which the waters prevailed. Later verses add further dates involving the drying of the ground, so the entire narrative lasts longer than either figure alone. The text presents a sequence of events rather than one single Flood duration.