Genesis states that rain fell on the earth for forty days and forty nights Genesis 7:12. The account also notes that the waters prevailed on the earth for 150 days Genesis 7:24.
After the seven-day waiting period, the flood finally arrives and does so on a precisely dated day in Noah’s life. The text describes the start of the catastrophe with two coordinated images: waters breaking up from below (“fountains of the great deep”) and waters pouring from above (“sky’s windows”). This unit sits in the middle of the flood narrative, immediately after God’s instructions and Noah’s entry into the ark with his household and the animals (earlier in Genesis 7:1–9).
Genesis 7:10–12 presents the flood as beginning at a set, identifiable time. After a seven-day wait, the waters arrive. The narrator then ties the start to Noah’s life by giving a specific date (year, month, and day).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Genesis 7:12, then read the surrounding section so the answer stays connected to the passage's flow.
12The rain was on the earth forty days and forty nights.