Gen. 15:13 had foretold that the time in Egypt would be 400 years. 400 is a round figure. The rabbis addressed themselves to the discrepancy by dating the 430 years from Abraham’s vision and the 400 from the birth of Isaac.
The Ramban (Moses Nachmanides) has another view – that 30 years were added to the original 400 because the people neglected commandments such as circumcision.
But how long did the actual enslavement last if the 430 (or 400) years dated from patriarchal times?
The sages said the enslavement was 210 years. The Haggadah informs us that “The Holy One blessed be He calculated the end – chishev et ha-ketz“; the numerical value of ketz is 190, i.e. God, out of compassion, deducted 190 years from the 400, leaving 210.
Targum Yonatan says, “The Children of Israel stayed in Egypt 30 times 7 years, i.e. 210 years; 430 years had elapsed from the time when God spoke to Abraham.”
According to the Septuagint, “The sojourn of the Children of Israel during which they dwelt in Egypt and in the land of Canaan was 430 years”.