A common challenge presented by skeptics or atheists to prove a biblical contradiction exists in the Flood account is: “How long did the flood last? Genesis 7:17 says it lasted 40 days, but Genesis 7:24 and 8:3 both say it lasted 150 days. So, which one is true?” Answering this claim requires reading the entire flood account in Genesis 7:1–Genesis 8:14. When these three verses in question are read and understood in context, they are not contradictory but describe a different aspect of the worldwide flood.

According to Genesis chapters seven and eight, the worldwide flood had three phases that took the earth's surface from dry land to dry land once again:

The first phase describes the 40 days and nights of continual rain and outpouring of water from the deep fountains of the earth that covered the world with water. This portion is what most people associate with "the flood" (Genesis 7:11-23).
The second phase describes the 150-day period from the start of the floodwaters to their end (40 days and nights) and the 110 days that followed when those amassed floodwaters remained covering the earth without receding (Genesis 7:24-8:4).
The third and final phase describes the period after the 150 days when God gradually decreased the floodwaters until the earth's surface was completely dry (Genesis 8:5-14).

Despite the floodwaters accumulating for only 40 days and nights and remaining on the earth for a few months afterward without receding, the entire length of the flood and its aftermath—from dry land to dry land—lasted one year and ten days. It began when Noah was 600 years, two months, and 17 days old (Genesis 7:11) and ended when Noah was 601 years, two months, and 27 days old (Genesis 8:13-14).

Therefore, contrary to what skeptics and atheists claim, there are no contradictions within the flood account.