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.
The 150-day period is not the same as the forty days and nights of rain. Genesis presents the rain as one stage, followed by a period during which the waters remained dominant. Later, Genesis 8 describes the waters gradually receding and the Ark coming to rest on the mountains of Ararat.
Readers sometimes combine every time marker into a single number, but the narrative separates them. The rain lasted forty days and nights, the waters prevailed for 150 days, and the complete process of drying took longer still. The text’s dates and intervals create a detailed sequence rather than a single short voyage.