In Genesis, the floodwaters prevailed over the Earth for 150 days.
Genesis 7:24 states that the waters prevailed upon the Earth for 150 days. This number describes the period during which the waters remained dominant, not simply the duration of rainfall. Genesis separately says that rain fell for 40 days and 40 nights, a distinction that explains why the two figures should not be treated as alternatives.
The chronology continues with the Ark resting on the mountains of Ararat in the seventh month and the mountain tops becoming visible in the tenth month. Those markers create a longer sequence than the 40-day rainfall alone. Translations may vary in phrasing, but the standard English figure in Genesis 7:24 is 150 days. The number is therefore a useful test of the narrative’s internal timeline.