Note 3 at Ac 7:6: This is the precise period of time that God prophesied to Abram in Ge 15:13. However, because Ex 12:40-41 clearly states that the children of Israel came out of Egypt after 430 years, some have argued that Ge 15:13, and this reference here, was only a round number, not intended to be accurate.

This difference of 30 years becomes very important, however, when the 40 years (Ac 7:30) Moses spent in the wilderness after his failed deliverance attempt is subtracted from the 430 years of actual bondage. This means that Moses killed the Egyptian in an attempt to deliver the Jewish people in the 390th year of their sojourn, or 10 years before the time period prescribed by God in Ge 15:13 was up. It is most probable that the 400 years spoken of by God in Ge 15:13, and also here, was the exact time the Lord had intended before He delivered the Jewish people from Egypt, but Moses' self-will that was exhibited in killing the Egyptian (Ex 2:12) cost Moses 40 years in the desert and the children of Israel 30 years of extra bondage.

The Israelites were not slaves in Egypt the entire 400 years. Abram came into Canaan when he was 75 years old (Ge 12:4). The covenant of Ge 15:13-16, which prophesied the 400 years, took place at least a year before Ishmael's birth (Ge 16:15). That means that Abram could not have been over 85 when this covenant was made (Ge 16:16 minus nine months), and he could have possibly been in his 70s. Abraham then had Isaac at 100 years of age. When Isaac was 60, Jacob and Esau were born (Ge 25:26), and Jacob moved to Egypt with his children when he was 130 years old (Ge 47:9). That was not more than 215 years but at least 205 years after the covenant of Ge 15 when God spoke of the 400 years that Abram's seed would be afflicted.

Joseph was 39 when his father, Jacob (or Israel), came into Egypt (Ge 41:46-47 and 45:6), and the Israelites enjoyed freedom throughout the rest of Joseph's life, another 71 years (Ge 50:22). That would bring the total elapsed time from the prophecy of Ge 15 to the death of Joseph to 276-286 years.

Ex 1:8 does not clearly state how long it was after the death of Joseph until another king arose who didn't know Joseph, but it can be assumed that it was at least a period of some years. That would mean that the total time the Israelites could have been slaves to the Egyptians was 150 years at most, and probably much less than that.

The first-century historian Josephus arrived at this same conclusion when he wrote that the Hebrews 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" (The Antiquities of the Jews, Book 2, Chapter 15, Section 2).