In the Noah's Ark account, the Flood waters prevailed over the earth for 150 days.
Genesis 7:24 states that the waters prevailed upon the earth for 150 days. This figure is distinct from the 40 days and 40 nights during which rain fell. The narrative uses several time markers to describe the Flood's progression, including the rising waters, the ark's resting, the appearance of mountain tops, and the eventual drying of the ground.
This distinction is one of the story's most common chronology questions. Forty days describes the stated duration of rain, while 150 days describes the period during which the waters prevailed. Neither figure alone represents the total time Noah and his family spent inside the ark.
Genesis 8 continues the chronology by saying that the waters decreased and that Noah eventually left the ark after receiving God's instruction. The narrative's detailed dates and intervals are why different Flood-duration summaries can seem to conflict when they actually refer to different stages.