In Parshat Bo we read (Shmot 12:40):
The habitation of B’nai Yisrael living in Egypt lasted 430 years.
Where did the number 430 come from?
According to Rashi, 430 is the sum total of all of the settlements of our forefathers in other lands plus their years in Egypt.
This is how Rashi breaks it down:
From the birth of Yitzchak until the Exodus from Egypt there were 400 years. We start counting from the birth of Yitzchak, for only from the time when Abraham had offspring from Sarah could the prophecy (Breisheet 15:13) “For your descendents will be foreigners in a land that is not theirs. They will enslave them and oppress them for 400 years” be fulfilled; and 30 years passed from the time that decree was made at the “Brit Ben HaBetarim”, “the covenant between the pieces” until the birth of Yitzchak.
It is impossible to say that the 430 years were in the land of Egypt alone, for Kehat (Levi’s son) was among those who came down to Egypt with Yaakov (Breisheet 46:11); If you calculate Kehat’s years (133) and all the years of Amram, his son (137) and the whole eighty years of Amram’s son, Moshe (at the time of the Exodus), they do not total to so many (133+137+80=350). In addition, Kehat had already lived many years before he went down to Egypt, and many of Amram’s years overlap with his father Kehat, as many of Moshe’s 80 years overlap with his father, Amram, so we do not find even 400 years from their coming to Egypt until the Exodus.
We must therefore admit that the other settlements of our forefathers in lands other than Egypt (in the land of Plishtim, Grar etc.) also come under the name of “sojourning as a stranger” (gerut), even in Chevron (which was in Canaan) because it is said, (Breisheet 35:27) “[Chevron] where Abraham and Yitzchak resided”, and it says, (Shmot 6:4) “[the Land Canaan], the land of their residing in which they resided temporarily”.
Therefore, the prophecy in Breisheet 15:13 “For your descendents will be foreigners in a land that is not theirs. They will enslave them and oppress them for 400 years” began only once Avraham had offspring. And only if you count the 400 years from the birth of Yitzchak will you find that from the time they came into Egypt until the time they left it, was 210 years.
Our verse was altered for King Ptolemy (Megillah 9a) who gathered 72 elders of Israel and placed them in 72 houses and he did not reveal to them at first why he gathered them. He told each one to write a Greek translation of the Torah. God placed council in each of their hearts and all of them independently arrived at a common decision about how to translate various words in the Torah.
The way that the 72 elders translated our passage as recorded in the Talmud Bavli Megillah 9b was: And the abode of B’nai Yisrael, which they stayed in Egypt and in other lands was 400 years.
The change in the number may have been to keep in line with the number 400 mentioned in the “Brit Ben HaBetarim.”
However the version in the Talmud Yerushalmi keeps the number at 430 years.
Either way, the elders certainly added “in Egypt and in other lands” in order to avoid confusion since B’nai Yisrael certainly did not stay in Egypt for 430 years.
According to Ibn Ezra, the extra 30 years are counted from the time that Avraham first left his home in Ur Kasdim and went to Charan. Avraham stayed with his father Terach in Charan for 5 years and arrived in the Land of Cnaan when he was 75. Yitzchak’s birth was 30 years after Avraham started on his journey which began at age 70.
We see from here that the 430 years include all of the travels of our forefathers from the first time that God appeared to Avraham until the Exodus from Egypt. It was only once B’nai Yisrael conquered and settled the Land of Israel with Yehoshua, after they wandered for 40 years in the desert, that the Land of C’naan officially belonged to them and became an eternal permanent rather than temporary dwelling place and homeland for the Jewish people.