Genesis says that 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 describes the period during which the waters remained dominant, not the forty days and forty nights of rainfall. The distinction is one of the clearest numerical features of the Genesis chronology.
After the 150-day period, Genesis 8 says that God caused a wind to pass over the earth and that the waters began to abate. The ark then came to rest on the mountains of Ararat, but Noah and his family still waited before leaving. The complete sequence therefore lasts longer than either forty or 150 days.
The numbers are often compressed in popular summaries of the story. “Forty days” refers to rain, while “150 days” refers to the waters prevailing. Both figures occur in Genesis, but they answer different questions about the Flood’s duration.