In Genesis, the Flood waters prevailed over the Earth for 150 days.
Genesis 7:24 states that the waters prevailed for 150 days after rising over the land. This is not the same measurement as the forty days and forty nights of rain. The text presents the rain as one phase and the continued dominance of the waters as a longer phase.
The narrative then records that God caused a wind to pass over the Earth, after which the waters began to recede. Genesis 8:4 says the ark came to rest on the mountains of Ararat in the seventh month, and the ground eventually became dry in the following year.
Readers sometimes combine the story’s numbers into one single duration. The biblical chronology contains several milestones: the rain, the prevailing waters, the ark’s resting, the appearance of mountain tops, and the final drying of the ground. The 150-day figure specifically belongs to the period when the waters prevailed.