Pinpointing the exact length of the Israelite sojourn in Egypt is a task that brings with it varying views, strong disagreement among scholars and enthusiasts, and yet the great opportunity to synchronize Israelite and Egyptian history with precision. The two prevailing views are that the Israelites resided in Egypt for 430 years and for 215 years. Apart from genealogies, the term "430 years" appears three times in the Bible (Exod 12:40, Exod 12:41, and Gal 3:17). Conversely, the term "215 years" does not appear in the Bible once, which should be an ominous sign for objective truth-seekers. The proper conclusion about the length of the Israelite pre-exodus residency in Egypt is that it comprised 430 years. I went to great lengths to prove this reality with the publication of my 2019 peer-reviewed journal article entitled, "Determining the Precise Length of the Israelite Sojourn in Egypt" (Near East Archaeological Society Bulletin 64 [2019]: 41-61), which is available as a free download from my academia.edu webpage.
Given that this article probably represents the most extensive study of the matter yet published, there is no reason to reproduce its contents or rehash the issues here. However, one of the topics within the article deserves a moment of attention here. Recently, several pastors--most of whom graduated from Dallas Theological Seminary--asked me about the validity of a chronological chart produced by Dr. Thom Constable regarding the term "about 450 years" found in Acts 13:17. Constable stretched these years from 1845 to 1395 BC, which makes for exactly 450 years. In the process, he suggested that the period of Israelite slavery in Egypt began in 1845 BC. Yet this valiant effort misses the mark on several matters. Below is my (corrected) version of the chart that my pastor friends received from Constable some years ago.
The first area of difference between my position and that of Constable is when Jacob's family entered Egypt. I date that event to 1876 BC, whereas he dates it to 1875 BC. The difference is extremely minor, but the reason for preferring 1876 BC is that (1) the exodus is known to have occurred on Friday, 24 April 1446 BC (Petrovich 2021: 23), and (2) the exodus took place exactly 430 years (to the very day!) after Jacob's family entered Egypt (Exod 12:40-41).
The second area of difference between my position and that of Constable is that whereas he takes the beginning of the "about 450 years" in Acts 13:17 as the start of the Israelite bondage in Egypt, I take it as the year of Jacob's family's entrance into Egypt, as the pre-bondage portion of the Israelite sojourn in Egypt is not to be excluded from the overall timeframe of the sojourn for Luke. Moreover, Constable arbitrarily chose 1845 BC as the year in which the bondage began. On what basis was this date chosen? Who was the king who arose in Egypt who did not know of Joseph (Exod 1:8)? This choice would place the outset of the bondage in the 12th Dynasty, the very dynasty during which Joseph was elevated. It is implausible to suggest that the king of Exod 1:8 reigned within the same dynasty as the abundance pharaoh and the famine pharaoh. This scenario of Constable simply cannot work within Egyptian history, as this alleged king of 1845 BC most certainly would have known who Joseph was.
The third area of difference between my position and that of Constable is that whereas he took the conquest under Joshua as ending in 1395 BC, I take it as ending in 1400 BC. In my Journal of the Evangelical Theological Society article on the destructions of Hazor under (1) Joshua, then (2) Deborah and Barak (Petrovich 2008: 495, ftn. 26), I attempt to prove that the conquest began in 1406 BC and ended in 1400 BC, as the campaign required six years of work rather than 11 years (per Constable's numbering). The conquest thus ended in the very year that most archaeologists consider to be the final year of the Late Bronze Age Ib in the Levant.
The fourth area of difference between my position and that of Constable is that while he assigned 400 years to the Israelite enslavement, I assign 114 years to it. The argumentation for this requirement involves a lot of evidence, all of which is found in my Origins of the Hebrews book, so it need not be repeated here, especially given the amount of space that would be required for a small blog entry. It can be summarized here that the bondage began in 1560 BC, the very year in which the native Egyptians of the 17th Dynasty completed the expulsion of the Hyksos and feared that the Israelites would join themselves to the surviving Hyksos who had fled from Egypt and were holed up at Sharuhen, in southern Canaan. The native Egyptian king's (Ahmose) solution to avoid this possibility was to enslave the Israelites.
For me, there are two possibilities for how to understand the "about 450 years" of Acts 13:17. With option #1, Luke was using the 430 years of Exod 12:40 in his equation for the length of the sojourn, which would end up making the "about 450 years" of the sojourn + wandering + conquest equal to 476 actual years, which is reasonably close to 450 years. With option #2, Luke was using the 400 years of Gen 15:13, which is a rough and non-literal number, in his equation for the length of the sojourn. If this was his intention, the numbers for the sojourn + wandering + conquest would equal 446 rough years, which is extremely close to the 450 years of Acts 13:17. While either option can work for the math, and for me, probably option #1 is more plausible. Why? Luke was a trusted companion of Paul, and Paul's use of the precise number "430 years" (equal to the length of the sojourn) in Gal 3:17 probably would have been forged into Luke's mind, which he would have used for the rough count that he offered in Acts 13:17.