In Genesis, the Flood waters prevailed over the earth for 150 days.
Genesis 7:24 gives this figure after describing the rising waters and the destruction of life outside the ark. Genesis 8:3 then says the waters began to recede after the 150 days. This is a different measurement from the 40 days and 40 nights of rain.
The distinction is one of the most frequent numerical mix-ups in the story. Forty days describes the rainfall, whereas 150 days describes the period during which the waters prevail. The narrative also supplies dated milestones that extend the whole episode considerably beyond either number.
Because biblical translations and chronological interpretations can differ over how the dated months are counted, the safest direct answer is the explicit duration stated in Genesis: 150 days for the waters’ prevailing.