Biblically speaking, the Israelites were in Egypt for 215 years, not 430 years.

Now the time that the sons of Israel had lived in Egypt was 430 years.

Exodus 12:40

Most Christians believe this because their Bibles say this plainly. Most Christians don't even bother to question this number, as with many things in their belief system. But this is actually not mathematically possible.

Moses was 80 years old when he and Aaron spoke to Pharoah (Exodus 7:8), which was significantly less than 1 year before the Israelites left Egypt. Their father Amram died at the age of 137 (Exodus 6:20). His father Kohath died at the age of 133 (Exodus 6:18). And Kohath was one of the 66 persons who came to Egypt with Jacob (Genesis 46:11,26).

So let's stretch this out as far as we possibly can. Let's assume that Kohath was a newborn baby when he came to Egypt, Amram was born the year Kohath died, and that Moses was born the year Amram died. 133 + 137 + 80 = 350. According to the Bible, the Israelites could not have been in Egypt for any longer than 350 years. Even when you stretch out the timeline as much as humanly possible, even to the point of proposing an absolutely ridiculous and blatantly unrealistic scenario, it still falls a whopping 80 years short. Clearly, the Israelites were not in Egypt for 430 years. They were in Egypt for significantly less than 350 years.

So how long were they really in Egypt? Well, Moses received the law 430 years after Abraham received the promise (Galatians 3:16-17). So the timeline begins when Abraham received the promise. Abraham was 75 years old when he received the promise and entered Canaan (Genesis 12:3-5,7). 25 years later, when Abraham was 100, Isaac was born (Genesis 21:5). 60 years later, Jacob was born to Isaac when he was 60 (Genesis 25:26). 130 years later, all of Israel entered Egypt (Genesis 47:9). 25 + 60 + 130 = 215. So, Israel entered Egypt 215 years after Abraham entered Canaan.

And because Moses received the law the same year Israel left Egypt, that means that the time Israel left Egypt marks the end of this timeline. 430 - 215 = 215, meaning that the Israelites were in Egypt for 215 years. That is mathematically possible, and it is significantly less than 350 years, meaning that no insane scenario needs to be proposed in order to say this.

So why does the Bible say they were in Egypt for 430 years, when this is not mathematically possible? Well, because all of our Bibles are translated from the Hebrew Masoretic text, which was copied between the 6th and 10th centuries. But there are other texts that account the same history.

The Greek Septuagint says, "And the sojourning of the children of Israel, while they sojourned in the land of Egypt and the land of Chanaan, four hundred and thirty years."

The Samaritan Pentateuch says, "Now the sojourning of the children of Israel and fathers of them, who dwelt in Canaan and in Egypt, was four hundred and thirty years."

Flavius Josephus said in Book II Chapter 15 paragraph 2 of Antiquities of the Jews, "They left Egypt...four hundred and thirty years after our forefather Abraham came into Canaan, but two hundred and fifteen years only after Jacob removed into Egypt."

All of these texts, which are all older than the Hebrew Masoretic text, bare witness to this timeline, in fact Flavius Josephus describes it exactly. In fact, technically the Hebrew Masoretic serves as a witness to this timeline, because of the numbers it puts forth in other verses, meaning that it bares witness against itself. So given the fact that many writings, which are all older than the Hebrew Masoretic text, testify to a different timeline than this one single writing, and given the fact that that single writing's timeline isn't even possible in the first place, this timeline is obviously the true one.

But the Israelites were enslaved for even less time than that. The Israelites were only enslaved after Joseph and all that generation died, and a new king arose who did not know Joseph (Exodus 1:6,8). Well Joseph was 30 years old when he entered Pharoah's service (Genesis 41:46). Shortly after that, the infamous 7 years of abundance and 7 years of famine occurred. So in the middle, Joseph was very likely 37 years old. It was 2 years later that Israel entered Egypt, because the famine had already been happening for 2 years (Genesis 45:6). This would make Joseph 39 years old when Isreal entered Egypt, and this begins the 215 years that they were in Egypt.

71 years later, Joseph died at the age of 110 (Genesis 50:22). This means that Egypt was under Joseph's rule for 71 years, and since they were not enslaved until after Joseph and all that generation died, they were not enslaved for this entire time. The Israelites were not enslaved for at least 71 years. Additionally, Moses was 80 when Israel left Egypt, and they were already slaves when he was born. 215 - 80 - 71 = 64, meaning there were 64 years in-between the death of Joseph and the birth of Moses. They were not slaves when Joseph died, but they were slaves when Moses was born, and the timeline ends 80 years after Moses was born. So they became enslaved at some point during a 64 year time period.

This gives us a final number of 112 ± 32 years, meaning that the Israelites were enslaved for 112 ± 32 years. And they were in Egypt for 215 years.

But what about the prophecy? Didn't God Himself tell Abraham that his descendants would be enslaved in Egypt for 400 years? No. Here's what He actually said: "Then God said to Abram, “Know for certain that your descendants will be strangers in a land that is not theirs, where they will be enslaved and oppressed for four hundred years." (Genesis 15:13). This prophecy is more specific than simply saying "Your descendants will be enslaved in Egypt for 400 years." And this extra piece of nuance is important.

Isaac, Jacob, and the multitudes in Egypt were all Abraham's descendants. Both Canaan and Egypt were lands that were not theirs. And they were oppressed during this time as well (Genesis 21:9, Galatians 4:29). And then of course the Israelites were enslaved.

Now, from Abraham receiving the promise to Moses receiving the law, there was 430 years. Isaac was born 25 years later, and he was weaned on the same day Ishmael scoffed at Isaac. In Talmudic times, it was customary to celebrate a child's weaning anywhere from 18 months to 5 years old. And if Isaac was weaned at 5 years old, then that means he was weaned 30 years after Abraham received the promise; which is exactly 400 years before Israel left Egypt. And this is when the oppression began. This is when the events God spoke about began.

God was right. Abraham's descendants was oppressed and enslaved in a land not theirs for exactly 400 years. Not any more, not any less. This is the real biblical timeline.

Conclusion: Biblically speaking, the Israelites were in Egypt for 215 years, and only enslaved for 112 ± 32 years. But God's prophecy was still true, because Abraham's descendants were enslaved and oppressed in a land not theirs for exactly 400 years. The Hebrew Masoretic text dropped the phrase "and Canaan" from the text, which has caused people to wildly misinterpret what really happened.