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Ask how long Israel was in Egypt and you will be told four hundred years, or four hundred and thirty, depending on who you ask. Both numbers are in scripture. They are not the same number, they are not measuring the same thing, and the gap between them moves Abraham by two centuries.
Two numbers, both in the text
Exodus 12:40 gives the figure most people remember: "Now the sojourning of the children of Israel, who dwelt in Egypt, was four hundred and thirty years."
Genesis 15:13 gives a different one. In the covenant made with Abram, he is told that his seed "shall be a stranger in a land that is not theirs, and shall serve them; and they shall afflict them four hundred years."
Stephen repeats the four hundred in Acts 7:6. So the Bible contains both figures, thirty years apart, and neither is presented as an approximation of the other.
Thirty years is a small discrepancy and easily absorbed — a round number against an exact one. The real problem is not the thirty. It is the question of what the four hundred and thirty years are counting.
The manuscripts do not agree
This is the part that usually gets left out, and it is the part that decides the argument.
The Hebrew text that stands behind most English Bibles is the Masoretic Text. It says the sojourning of Israel in Egypt was 430 years.
The Septuagint — the Greek translation made by Jewish scholars in Egypt from the third century BC onwards — says something longer. Its version of Exodus 12:40 reads that the sojourning of the children of Israel which they sojourned in the land of Egypt and in the land of Canaan was 430 years.
The Samaritan Pentateuch agrees with the Septuagint. Canaan is in the total.
Those few extra words do all the work. On the Masoretic reading, the clock starts when Jacob's family goes down to Egypt. On the Septuagint and Samaritan reading, it starts when Abraham enters Canaan, and Egypt accounts for only the back half of it.
Halve the number and you halve the problem, or you double it, depending on which difficulties you would rather carry.
Paul counts from a different starting point
Galatians 3:17 has Paul reckoning 430 years from the covenant with Abraham to the giving of the law at Sinai.
That is the Septuagint arithmetic. Paul is writing to Greek-speaking congregations who read the Greek scriptures, so this is not surprising, but it does mean a New Testament writer treats the 430 as covering Canaan and Egypt together rather than Egypt alone.
If you take Paul at face value, the Egyptian sojourn on its own is closer to two hundred years than four hundred.
The genealogy is too short
There is a second problem, and it is internal to the Hebrew text rather than imported from a translation.
Exodus 6 gives the line from Levi to Moses: Levi, then Kohath, then Amram, then Moses. Four names. Numbers 26 gives the same line. Kohath is listed among those who came into Egypt with Jacob, and Moses is eighty at the Exodus.
Four generations do not comfortably fill 430 years. They fill 215 rather better, and even that is stretched. The text gives lifespans for Kohath and Amram, but a father's lifespan does not tell you how old he was when the relevant son was born, so the sum cannot be closed from the numbers given.
Against that sits Genesis 15:16, which says the fourth generation shall come back to Canaan. Four generations is exactly what Exodus 6 lists. On the short reading the genealogy and the prophecy agree with each other without any strain at all.
The counter-argument is that biblical genealogies frequently skip. "Son of" can mean descendant, and lists are often shaped for symmetry rather than completeness. A four-name list is not proof of four biological generations.
That is a real point, and it is the one defenders of the long sojourn lean on. It is also, it has to be said, an argument that the list does not mean what it appears to mean.
The case for 430 years in Egypt
The long reading has the plainest text on its side. Exodus 12:40 in Hebrew says Egypt, and says 430, and the reader who wants the simplest possible handling of the verse in front of them will take it.
It also makes better sense of the population. Israel enters Egypt as seventy people and leaves as a nation large enough to alarm a pharaoh. Four centuries gives that growth room to happen at ordinary rates. Two centuries requires it to be remarkable.
And it fits Genesis 15:13 without adjustment. Four hundred years of affliction in a land not theirs reads naturally as four hundred years in Egypt.
The case for 215
The short reading has the Septuagint, the Samaritan Pentateuch, Paul, and the genealogy.
It also has a certain tidiness. Abraham enters Canaan; 215 years later Jacob's family goes down to Egypt; 215 years after that they come out. The covenant period divides in half at the descent into Egypt.
Its weakness is the population, and it is a serious one. Getting from seventy people to a nation in two centuries, through four generations, is a stretch that has to be argued rather than assumed.
Jewish tradition has generally gone this way. So did a good deal of early Christian chronology. Ussher took the short reading, which is why his Exodus sits where it does.
What the timeline does with it
We do not pick a winner quietly. Where the choice between 430 and 215 moves an event, the event carries the range and says which reading produced which date.
That is less satisfying than a single number, and it is the honest position. A reader who wants Abraham at a particular year can have one, but they should know they are choosing a manuscript tradition when they take it, and that careful readers have gone the other way for two thousand years.
The wider problem — why any two Bible chronologies disagree at all — is set out in why Bible chronologies disagree. The knock-on question of where the Exodus itself lands is in when did the Exodus happen.