How long were the Israelites sojourners in Egypt? Paul assigns a 430-year interval between the Abrahamic covenant given in Genesis and the Mosaic Law introduced at Sinai. The arithmetic gets knotty when one subtracts the 215-year period between Abraham and Jacob's migrations into Egypt from the aforementioned 430 years. We are then left with a 215-year captivity. However, this "short captivity" is difficult to square in light of Stephen's recounting of the 400-year bondage that the Lord decrees in Genesis 15:13-16 and Exodus 12:40. Josephus' account is equally puzzling: He describes a 400-year enslavement (War V), only to later posit a 215-year span (Antiquities II). Does my chronometer need a recalibration, or does the apostle have something else in mind (Galatians 3:17)?
Thank you for your question, and I am impressed by your research. While I am not going to answer your question directly, I would like to make some general comments concerning biblical chronology.
I am sure your chronometer is just fine. The problem may be you have a modern chronometer. For you a year is just a year -- 365.25 days. There has been much written on the question of the Israelites' time in Egypt, and many theories have been put forth to reconcile what seems to be a contradiction in chronology. None of these theories can claim to be the definitive answer. What these definitively do show is that there is no necessary contradiction. As long as there is a plausible harmonization, there can be no certain claim of a contradiction. In other words, whatever the actual answer, biblical inerrancy is not in danger.
Personally, I am comfortable simply saying that, while 1 year is 1 year to our modern minds, numbers often had a symbolic meaning in the Bible. That is not to say that a biblical number is never just a number; I only mean that a biblical number is not necessarily tied to the actual mathematical amount. It may be intended to communicate something less precise or more theological. This seems particularly true with numbers in Genesis. Now someone is sure to say, "Why should I read 430 years as anything besides 430 years?" The problem is that we often read from modern expectations. But the Bible is first-and-foremost a historical document. It is God's self-revelation given in time. It is never correct to read an ancient text from modern categories and genre expectations. A great rule of thumb is: If the text wouldn't have contradicted the original reader's expectations, it shouldn't contradict ours. I am sure that Luke, Stephen, and any number of their readers and hearers could count to 430 just as well as we can, yet they felt no need to explain, justify, or correct the ancient chronology. Obviously, this apparent discrepancy didn't cause them any concern, so neither should it for us. For many of us, it might not be our chronometers that need recalibrating as much as the expectations we bring to the biblical text.
For more on how to read the Bible in its own context, please see How to Read the Bible for All its Worth by Fee and Stuart.
--IBTM Research Team